Sustainable Wells: Maintenance, Problem Prevention, and Rehabilitation

SUSTAINABLE WELLS Maintenance, Problem Prevention, and Rehabilitation SUSTAINABLE WELLS Maintenance, Problem Preventi...

Author: Stuart A. Smith | Allen E. Comeskey

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SUSTAINABLE WELLS Maintenance, Problem Prevention, and Rehabilitation

SUSTAINABLE WELLS Maintenance, Problem Prevention, and Rehabilitation Stuart A. Smith Allen E. Comeskey

Boca Raton London New York

CRC Press is an imprint of the Taylor & Francis Group, an informa business

CRC Press Taylor & Francis Group 6000 Broken Sound Parkway NW, Suite 300 Boca Raton, FL 33487-2742 © 2010 by Taylor and Francis Group, LLC CRC Press is an imprint of Taylor & Francis Group, an Informa business No claim to original U.S. Government works Printed in the United States of America on acid-free paper 10 9 8 7 6 5 4 3 2 1 International Standard Book Number: 978-0-8493-7576-7 (Hardback) This book contains information obtained from authentic and highly regarded sources. Reasonable efforts have been made to publish reliable data and information, but the author and publisher cannot assume responsibility for the validity of all materials or the consequences of their use. The authors and publishers have attempted to trace the copyright holders of all material reproduced in this publication and apologize to copyright holders if permission to publish in this form has not been obtained. If any copyright material has not been acknowledged please write and let us know so we may rectify in any future reprint. Except as permitted under U.S. Copyright Law, no part of this book may be reprinted, reproduced, transmitted, or utilized in any form by any electronic, mechanical, or other means, now known or hereafter invented, including photocopying, microfilming, and recording, or in any information storage or retrieval system, without written permission from the publishers. For permission to photocopy or use material electronically from this work, please access www.copyright. com (http://www.copyright.com/) or contact the Copyright Clearance Center, Inc. (CCC), 222 Rosewood Drive, Danvers, MA 01923, 978-750-8400. CCC is a not-for-profit organization that provides licenses and registration for a variety of users. For organizations that have been granted a photocopy license by the CCC, a separate system of payment has been arranged. Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation without intent to infringe. Library of Congress Cataloging-in-Publication Data Smith, Stuart A. Sustainable wells : maintenance, problem prevention, and rehabilitation / Stuart A. Smith and Allen E. Comeskey. p. cm. Includes bibliographical references and index. ISBN 978-0-8493-7576-7 1. Wells--Maintenance and repair. I. Comeskey, Allen E. II. Title. TD407.S663 2010 628.1’14--dc22 Visit the Taylor & Francis Web site at http://www.taylorandfrancis.com and the CRC Press Web site at http://www.crcpress.com

2009019275

Contents List of Tables and Figures....................................................................................... xiii Disclaimer................................................................................................................xxi Preface.................................................................................................................. xxiii Authors..................................................................................................................xxvii Acknowledgments..................................................................................................xxix Chapter 1. A Brief Colorful History of Well Maintenance and Rehabilitation and Their Milestones.....................................................1 1.1 1.2 1.3 1.4 1.5

Some History..............................................................................1 The Role of the “Environmental” Sector in Shaping Well Rehabilitation and Maintenance........................................5 The Impact of Biology on Hydrogeology and GroundWater Technology.......................................................................6 Economics, Human Skills, Personalities, Demographics, and Other Issues.........................................................................8 A Word about Terminology...................................................... 11

Chapter 2. Causes and Effects of Well Deterioration........................................... 13 2.1 2.2 2.3 2.4 2.5 2.6 2.7

Summary: Causes of Poor Performance.................................. 13 True Grit—Sand and Silt.......................................................... 13 Yield and Drawdown Problems................................................ 17 Chemical Incrustation..............................................................20 Corrosion.................................................................................. 22 Plastic Deterioration.................................................................26 Biofouling—A Hitchhiker’s Guide to How Life Takes Over................................................................................26 2.7.1 Biofilm and Biofouling Basics..................................... 27 2.7.1.1 Biofilms and Microbial Survival................. 29 2.7.1.2 Biofilm Function and Ecological Function....................................................... 30 2.7.1.3 Biofilms and Biofouling in Ground Water............................................................ 30 2.7.2 Water Quality Degradation: Monitoring and Remediation Problems................................................ 33 2.7.3 Microbially Mediated Metallic Corrosion.................. 37 2.7.4 Iron, Manganese, and Sulfur Biofouling..................... 39 2.7.4.1 Fe, Mn, and S Biofouling: What’s Happening.................................................... 39 2.7.4.2 How Fe, Mn, and S Biofouling Occurs.......40 2.7.4.3 The Redox Fringe........................................ 42 v

vi

Contents

2.7.5

Effects on Performance of Well Systems: A Summary..................................................................... 43 2.7.5.1 Hydraulic Impacts........................................46 2.7.5.2 Sample Quality in Monitoring Wells........... 47 2.7.5.3 ASR Well Systems....................................... 47 2.7.6 Health Concerns Relating to Biofouling..................... 48 2.7.6.1 Pathogens..................................................... 48 2.7.6.2 Toxic Accumulation..................................... 49 2.7.6.3 Chlorination of Organic Chemicals............. 49 2.8 Impacts on Treatment Plants.................................................... 49 2.9 Engineering and Construction Aggravation of Clogging and Corrosion........................................................................... 50 2.10 Well Structural Deformation and Failure: Natural and Human Caused......................................................................... 51 2.10.1 Natural......................................................................... 51 2.10.1.1 Earthquakes................................................. 51 2.10.1.2 Mass Wasting............................................... 53 2.10.2 Human Induced........................................................... 55 2.10.2.1 Mining......................................................... 55 2.10.2.2 Mine Blasting.............................................. 56 2.10.2.3 Grouting....................................................... 57 2.10.2.4 Casing Weight/Quality/Integrity/ Engineering Issues....................................... 59 2.10.2.5 Improper Rehabilitation and Development Methods, and Other Abuses of Wells........................................... 61 2.10.2.6 Electrochemical Corrosion from Stray Potentials..................................................... 62 2.10.2.7 And Other Factors ….................................. 63 2.11 Disaster-Related Flooding........................................................64 2.12 Management and Operational Overview.................................. 65 Chapter 3. Economic Impacts of Well Deterioration............................................ 67 3.1

3.2 3.3

3.4

Identifying Costs of Well Deterioration................................... 67 3.1.1 Defining Economic Parameters.................................. 67 3.1.2 Types and Dimensions of Costs of Well Operation and Service................................................. 69 Asset Management and Life Cycle Cost.................................. 73 3.2.1 Asset Management Features of Well Systems............ 74 3.2.2 Life Cycle Costs.......................................................... 75 Assigning Economic Value...................................................... 76 3.3.1 Water Supply EV......................................................... 77 3.3.2 Other Environmental EV............................................ 77 3.3.3 Government Accounting Valuation of Assets............. 78 A Costly Example..................................................................... 78

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Contents

Chapter 4. Prevention Practices for Sustainable Wells......................................... 81 4.1 4.2 4.3

Prevention—Its Place in the Well Life Cycle........................... 81 Interlude: Teeth and Motor Vehicles........................................ 82 Prevention: Design and Construction Considerations..............84 4.3.1 Planning Considerations..............................................84 4.3.2 Role of Well Purpose.................................................. 86 4.3.3 Well Design................................................................. 86 4.3.4 Casing for Well Completion........................................ 87 4.3.5 Well Hydraulics and Efficiency—General Considerations............................................................. 89 4.3.6 Well Screens and Intakes............................................90 4.3.6.1 Screen Design.............................................. 91 4.3.6.2 Screen and Filter Pack Material Selection....................................................... 91 4.3.7 Grouting and Well Sealing.......................................... 93 4.4 Well Development....................................................................94 4.4.1 Reasons for Development............................................94 4.4.2 Development Method Descriptions............................. 95 4.4.2.1 Overpumping...............................................96 4.4.2.2 Surging and Pumping or Bailing (Utilizing Surge Block)................................96 4.4.2.3 Airlift Development.....................................99 4.4.2.4 Jetting......................................................... 100 4.4.3 “Conventional” Development Choices...................... 102 4.4.4 Fluid-Pulse Development.......................................... 104 4.4.5 Other Care Issues in Development and Redevelopment.......................................................... 105 4.5 Preventing Contamination during Drilling, Well Construction, and Development............................................. 105 4.6 Preventative Pump Choices and Actions................................ 106 4.6.1 Pump Selection.......................................................... 107 4.6.1.1 Pumps in Water Supply and Other Extraction (or Abstraction) Wells.............. 107 4.6.1.2 Pumps in Monitoring Wells....................... 108 4.6.2 Pump Protection........................................................ 110 4.7 Design Aspects: The “Cliff Notes” Version........................... 113 4.8 A Note about Well Houses..................................................... 114 4.9 Well Array Design Recommendations................................... 115 4.10 A Developing World Note...................................................... 116 Chapter 5. Maintenance Monitoring Programs for Wells.................................. 119 5.1 5.2

Maintenance Monitoring: Rationale for Instituting a Monitoring Program............................................................... 119 Maintenance Procedures Overview....................................... 122

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Contents

5.3 5.4 5.5

5.6

5.7

Implementing a Maintenance Program—It’s Institutional, Not Personal...................................................... 122 Maintenance Is Personal (and Personnel), Too....................... 122 Maintenance Basics................................................................ 123 5.5.1 Well System Maintenance Records........................... 123 5.5.2 Maintenance Monitoring for Performance and Water Quality............................................................ 124 5.5.3 Maintenance Actions and Treatments....................... 125 A Maintenance Monitoring Protocol for Wells...................... 126 5.6.1 Purposes of Maintenance Monitoring....................... 127 5.6.2 Background for Current Monitoring Recommendations..................................................... 127 5.6.3 Deciding How to Monitor......................................... 128 5.6.3.1 Incorporating PM Data Collection into the Facility Data Collection Effort............ 130 Recommended Testing and Information Monitoring Methods.................................................................................. 130 5.7.1 Visual and Other Sensory Examination.................... 130 5.7.2 Well and Pump Performance.................................... 131 5.7.2.1 Benchmarking........................................... 132 5.7.2.2 Compare Apples with Apples.................... 136 5.7.2.3 Monitoring Pump and Pump Motor Performance............................................... 137 5.7.2.4 Tracking Well Performance....................... 137 5.7.2.5 Water Level Measurement Recommendations..................................... 139 5.7.2.6 Well Discharge Measurement.................... 139 5.7.2.7 Pressure Measurement............................... 141 5.7.2.8 Electrical (Power)...................................... 141 5.7.3 Water Sampling......................................................... 142 5.7.4 Physicochemical Analyses........................................ 142 5.7.5 Biological Monitoring: Decision Making................. 143 5.7.5.1 Whether to Monitor for Biofouling............ 144 5.7.5.2 Biofouling Monitoring: What Methods to Choose................................................... 144 5.7.5.3 A Note about the Current State of the Art in Well Maintenance Monitoring Methods.................................. 144 5.7.6 Biofouling Monitoring Methods: Analysis............... 145 5.7.6.1 Microscopic Examination and Analysis.... 145 5.7.6.2 Culturing Methods.................................... 146 5.7.6.3 How Minimal Can Testing Be?................. 149 5.7.7 Biofouling Monitoring Methods: Sampling Methods..................................................................... 151

Contents

ix

5.7.7.1 Pumped Sampling...................................... 151 5.7.7.2 Surface Collection on Slides or Coupons..................................................... 152 5.7.7.3 Representativeness of Collection Sampling.................................................... 153 5.7.8 Electrochemical In-line Sensors............................... 155 5.8 Summary of Recommendations for Maintenance Monitoring in Routine Practice.............................................. 156 5.8.1 Summary of Data Collection Requirements............. 156 5.8.2 Well Data File Features............................................. 156 5.8.3 Pumping Rates.......................................................... 157 5.8.4 System Pressure......................................................... 157 5.8.5 Water Level Data....................................................... 157 5.8.6 Electrical (Power) Data............................................. 158 5.8.7 Video for Historical Comparison.............................. 158 5.8.8 Hydrogeologic Information That Should Be on File............................................................................. 158 5.8.8.1 Piezometric Data....................................... 158 5.8.8.2 Piezometric Maps...................................... 159 5.8.8.3 Geologic Regime....................................... 159 5.8.9 Development Data..................................................... 159 5.8.10 Maintenance Logs for Individual Wells.................... 161 5.8.10.1 Where Records Should Be Kept................ 161 5.8.10.2 Downtime History..................................... 161 5.8.10.3 File Records Purpose and Format Issues.......................................................... 162 5.9 Schedule of Maintenance Monitoring Actions for Wells....... 163 5.9.1 Minimum Regular Schedule for First Year............... 163 5.9.2 Schedule for Reducing Maintenance Monitoring after First Year.......................................................... 163 5.9.3 Rationale and Commentary...................................... 165 5.10 Institutional and Funding Issues in Maintenance Planning, Analysis, and Execution......................................... 165 5.10.1 Background and Barriers to Effective Maintenance Implementation.................................... 165 5.10.2 Institutional Needs for Effective Implementations........................................................ 167 5.10.3 Quarterly Review of Facility Performance Data....... 168 5.10.4 Baseline and Historical Data for Wells/Site.............. 168 5.10.5 Operator/Working Crew Leader Qualifications and Training.............................................................. 169 5.10.6 Determination of Operational Maintenance Responsibilities......................................................... 170

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Contents

Chapter 6. Preventive Treatments and Actions................................................... 171 6.1 6.2 6.3 6.4 6.5

Sand/Sediment Pumping........................................................ 171 What Do We Do if We Have Corrosion?................................ 172 Biofouling (General)............................................................... 174 Inorganic Encrustations (General)......................................... 174 Preventive Chemical Treatments............................................ 174 6.5.1 General: Cost-Effectiveness, Professionalism........... 174 6.5.1.1 Cost-Effectiveness..................................... 175 6.5.1.2 Professionalism.......................................... 176 6.5.2 Chemical Classes and Properties.............................. 176 6.5.2.1 Acids for Maintenance Treatment............. 176 6.5.2.2 Biocides and Oxidizing Compounds......... 176 6.5.2.3 Penetrating, Sequestering, and Dispersing Agents...................................... 181 6.5.2.4 Blended Method Treatments...................... 181 6.5.3 Use and Interpretation of MSDSs............................. 182 6.5.4 Compatibility with Well Cleaning Chemicals.......... 183 6.6 Mechanical Agitation and Augmentation.............................. 183 6.7 Chemical Emplacement.......................................................... 184 6.8 Chemical Removal and Recovery.......................................... 184 6.9 In Situ Maintenance Treatment Techniques........................... 185 6.9.1 Chemical Feeders in Wells........................................ 185 6.9.2 Radiation—That Gentle Glow................................... 185 6.9.3 Application of Electromagnetically Charged Surfaces..................................................................... 186 6.9.4 CO2 Well Environment Adjustment—Making the Environment Inhospitable for Biofouling....................................... 186 6.10 Further Procedural Requirements.......................................... 187 6.10.1 Regulatory Aspects................................................... 187 6.10.2 Biofouling Recurrence.............................................. 187 6.11 Health and Safety Concerns................................................... 187 6.11.1 Health and Safety Plan.............................................. 187 6.11.2 Level of Protection for Mixing and Well Application................................................................ 188 6.11.3 Chemical Handling Hazards..................................... 188 6.11.4 Mixing Chemicals—Personal Safety Aspects.......... 188 6.12 Costs and Time of Routine Preventive Measurements........... 189 6.12.1 Maintenance Cost-Benefit Analysis.......................... 189 6.12.1.1 Cost-Benefit Analysis: A Spreadsheet Approach.................................................... 189 6.12.1.2 The Heartbreak of Well Failure: An Overriding Weighting Factor..................... 190 6.12.2 Costs of Maintenance Activities............................... 192

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Contents

6.12.2.1 Maintenance Monitoring Costs— Typical....................................................... 192 6.12.2.2 Preventive Treatment Costs....................... 194 6.12.3 Improving Cost-Effectiveness in Maintenance......... 194 Chapter 7. Rehabilitation and Reconstruction Planning..................................... 197 7.1 7.2

7.3

7.4

7.5

7.6

Decisions on Rehabilitation Methods: After Things Go Wrong..................................................................................... 197 Management and Safety in Well Rehabilitation..................... 198 7.2.1 Facility Management Considerations........................ 198 7.2.1.1 Responsibility for the Work....................... 199 7.2.1.2 Getting the Job Done.................................200 7.2.2 Safety and Productivity in Well Rehabilitation Work.......................................................................... 201 7.2.2.1 Safety Assurance....................................... 201 7.2.2.2 Facilitating Productivity............................202 7.2.3 Rehabilitation Contractor Considerations.................203 7.2.3.1 Safety: What the Contractor Needs to Have and Know......................................... 203 7.2.3.2 Practical Stuff: Access and Response.......205 Contractors and Consultants: Avoiding Trouble in Working Together...................................................................208 7.3.1 Mutual Respect in Rehabilitation Work....................208 7.3.2 Specifications: Business and Bidding Considerations...........................................................208 7.3.2.1 Specification Pitfalls..................................208 7.3.2.2 Overcoming Pitfalls...................................209 7.3.2.3 Effluent Waste Water Containment........................... 210 Well Rehabilitation: Decision Making on Methods............... 210 7.4.1 To Rehab or Not to Rehab? That Is the Question...... 210 7.4.2 The Costs of Well Rehabilitation.............................. 213 7.4.2.1 The Cost of Doing Nothing....................... 213 7.4.2.2 Costs for Serious Rehabilitation Work...... 214 7.4.2.3 Contractor Pricing of Rehabilitation Work.......................................................... 215 7.4.3 Choosing Rehabilitation Methods............................. 216 7.4.4 Damage...................................................................... 217 7.4.5 Issues in Rehabilitation Chemical Selection............. 218 7.4.6 Reconstruction........................................................... 220 Specifications for Rehabilitation............................................ 221 7.5.1 Specification Deficiencies......................................... 221 7.5.2 What Well Rehabilitation Specifications Should Have........................................................................... 225 7.5.3 Selecting Well Rehabilitation Bids............................ 226 The Role of Consultant Specifier-Observer............................ 227

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Contents

Chapter 8. Rehabilitation Methods..................................................................... 229 Chapter Technical Descriptions............................................................................ 229 8.1

8.2

8.3 8.4 8.5 8.6

Physical Agitation................................................................... 229 8.1.1 Basic Principles......................................................... 229 8.1.2 “Conventional” Redevelopment................................ 229 8.1.3 Other or Advanced Physical Redevelopment Methods..................................................................... 231 8.1.3.1 Cold CO2 Treatment................................... 231 8.1.3.2 Sonic/Vibratory Disruption—“Use the Force, Luke!”............................................. 233 8.1.3.3 Fluid-Pulse Tools....................................... 236 The Pharmacopoeia: Chemical Use in Rehabilitation...........240 8.2.1 Overview...................................................................240 8.2.2 Acidizing................................................................... 243 8.2.2.1 Types of Acid Compounds........................ 243 8.2.2.2 Using Acidizing in Well Treatment........... 245 8.2.3 Sequestering and Other PSDD Functions................. 247 8.2.4 Antibacterial (Antimicrobial) Agents.......................248 8.2.4.1 Chlorination...............................................248 8.2.4.2 Alternatives to Chlorine as Oxidants for Biofouling............................................. 252 Blended Method Treatments.................................................. 254 Application of Rehabilitation Methods Summary................. 256 Posttreatment after Well Rehabilitation................................. 257 Some Follow-up “Truisms”.................................................... 257

Chapter 9. Learning and Going Forward............................................................ 263 9.1 9.2

Learning from the Past........................................................... 263 Where Do We Go from Here?................................................264 9.2.1 Wish List................................................................... 265 9.2.2 Education, Communication, and Mutual Respect: Human Issues in Well Maintenance...........266

Recommended Reading List................................................................................ 269 Recommended Reading List............................................................. 269 Selected References........................................................................... 272 Selected Relevant Standards.............................................................. 277 ANSI/ASTM Standards (a selection)..................................... 278 Index....................................................................................................................... 279

List of Tables and Figures List of Tables Table 2.1

Categories of Well Problems and Related Causes.......................... 14

Table 3.1

Costs of Pumping (Per Year and Per Unit Volume)........................ 71

Table 4.1

General Well Design and Placement Guidelines............................ 85

Table 4.2

Casing Types and Choices...............................................................90

Table 4.3

Cathodic-Anodic Series of Metal Alloys........................................ 93

Table 5.1

Troubleshooting Summary Guide for Well Maintenance............. 125

Table 5.2

Parameters Useful in Well Maintenance Monitoring................... 126

Table 5.3

Features of Water Level Measurement Methods........................... 140

Table 5.4

ummary of Physicochemical Methods Relevant to Well S Maintenance.................................................................................. 143

Table 5.5

First-Year PM Monitoring Schedule............................................. 164

Table 5.6

Long-Term PM Monitoring Schedule........................................... 166

Table 6.1

cid Effectiveness, Safety and Handling—Recommended A Compounds.................................................................................... 177

Table 6.2

ommon Well Cleaning Chemicals in Use—Not C Recommended (USACE).............................................................. 178

Table 6.3

Well Treatment Chemical Incompatibility.................................... 182

List of Figures Figure 1.1

lephant digging for water in sand. (Tarangire National Park, E Tanzania)...........................................................................................2

Figure 1.2

ump impellers clogged by oxidized iron deposition. P Extraction well, DOE Fernald Preserve (Ohio).................................6

Figure 2.1

Impellers destroyed by pumping sand and gravel (Mexico)........... 15

Figure 2.2 Precleaning flow from a clogged well............................................. 17 Figure 2.3 W ell screen clogged by iron biofouling (North Dakota State University Extension, Scherer, 2005, Circular AE 97)................... 18 xiii

xiv

List of Tables and Figures

Figure 2.4 Pumping well yield and drawdown components............................. 18 Figure 2.5 O xidation and reduction and ecology changes around pumping wells................................................................................. 19 Figure 2.6 P ipe clogged by iron mineral (U.S. Environmental Protection Agency)............................................................................................20 Figure 2.7 Schematic of well with gas pressure release................................... 21 Figure 2.8 M ineral-clogged drain—mostly calcite (photograph courtesy of Chuck Cooper, Bureau of Reclamation)..................................... 22 Figure 2.9

Corroded submersible pump end (southern Colorado).................... 23

Figure 2.10 Diagram of a corrosion tubercle in steel pipe.................................24 Figure 2.11 C ross section of steel pipe corrosion tubercles (Lytle, Gerken, and Maynard, 2004, U.S. EPA).......................................................25 Figure 2.12 M ixed biofilm from water well samples (normal light photomicrograph)............................................................................28 Figure 2.13 Examples of manifestations of biofouling....................................... 29 Figure 2.14 Z ebra mussel fouling in pipe (Gemma Grace, Ontario, Canada)............................................................................................ 29 Figure 2.15 B acterial size, movement, and attachment in relation to pore size in aquifer materials (U.S. Geological Survey)......................... 31 Figure 2.16 I ron-related biofilm from well water samples (normal light photomicrograph)............................................................................ 31 Figure 2.17 Soil-water-oil-biofilm interface....................................................... 32 Figure 2.18 Microbial ecology schematic of a remediation system................... 33 Figure 2.19 P assage of a contaminant plume in an alluvial aquifer. This is a simulation based on observed phenomena, usually indications of microbial activity are detected months or years later in response to some observed problem...................................34 Figure 2.20 F e, Mn, and S transformations and mobility in aquifers—a schematic of typical occurrences in a biologically active mixed reducing-oxidizing aquifer system....................................... 35 Figure 2.21 F e transformation and plugging zone around an affected well—a schematic of the many activities and results of activity in the busy environment of a pumping well....................... 35 Figure 2.22 M icrobial corrosion processes schematic—illustrating the range of bio-electrical activity around a corrosion tubercle on a steel surface (some features also apply to crevice corrosion of stainless steel alloys)................................................................... 37


xv

Figure 2.23 E xample of mild steel well pump discharge pipe tuberculation.................................................................................... 38 Figure 2.24 M icrobially influenced corrosion of Type 316 stainless steel monitoring well casing. Section at left has begun anodic attack under biofilm associated with bentonite grout, while in the section on the right, corrosion is associated with metal fatigue..... 38 Figure 2.25 G allionella-dominated water well biofilm (normal light photomicrograph)............................................................................40 Figure 2.26 M ixed filamentous biofilm featuring MnIV oxide mineralogy (normal light photomicrograph (PMG)).......................................... 41 Figure 2.27 F ilamentous Mn-precipitating bacteria reemerging when MnIV oxide particles (black) are rehydrated (Bureau of Reclamation–Stuart Smith PMG, annotated by SAS)— minutes after adding water.............................................................. 42 Figure 2.28 S ulfur oxidizing biofouling in well pump discharge pipe, South Africa (Courtesy of Hose Solutions Inc.).............................. 42 Figure 2.29 T hothrix-dominated sulfur-oxidizing biofouling of geotechnical drains (Bureau of Reclamation–Stuart Smith photographs).................................................................................... 43 Figure 2.30 W hite sulfur biomass associated with artesian spring (in actuality, an uncontrolled well) in western Ohio............................ 45 Figure 2.31 S chematic presentation of the initiation and development of a biofilm (P. Dirckx, Montana State University Center for Biofilm Engineering)....................................................................... 45 Figure 2.32 E xtensively tuberculated pipe interior (Argentina: photo by Miguel A. Gariboglio).....................................................................46 Figure 2.33 Some causes of well structural failure............................................ 52 Figure 2.34 S lope and rail line affected by soil creep (Courtesy U.S. Geological Survey).......................................................................... 53 Figure 2.35 Slope affected by slump (Courtesy U.S. Geological Survey).......... 54 Figure 2.36 Shoreline erosion processes, Ashtabula County, Ohio.................... 54 Figure 2.37 H ouse foundation undermined by collapse of mining cavities (Pennsylvania Dept. of Environmental Protection photo)............... 55 Figure 2.38 L ong-wall mining effects diagram (Pennsylvania Dept. of Environmental Protection).............................................................. 55 Figure 2.39 P VC casing distorted by heat due to improper cement grouting (photo by Gary L. Hix). The casing is pushed in and cracked at the visible joint and the foreground surface is blistered.............. 58

xvi


Figure 2.40 Monitoring well casing bent due to vehicle collision...................... 62 Figure 2.41 P VC water well casing broken due to vehicle strike in parking lot. There was an attempt to fix it with a rubber boot coupling and protect it with a tire. This was a public water supply (bowling alley, now closed) in Ohio.................................... 62 Figure 2.42 F looding in the St. Mary’s River watershed (Ohio) (NOAA photo)...............................................................................................64 Figure 3.1

The meter is running....................................................................... 68

Figure 4.1

The well life cycle continuum......................................................... 82

Figure 4.2 S ome types of connections used in well casing and pump discharge pipe. (a) bell-end PVC casing pipe and (b) splinelock coupling (Certain Teed CertaLok™)...................................... 88 Figure 4.3 The necessary in-and-out motion of proper well development.......96 Figure 4.4

Example surge blocks (both double surge block tools)...................97

Figure 4.5 E xample well cleaning brush (manufactured by Cotey Chemical Corp., figure courtesy of Kevin McGuiness).................. 98 Figure 4.6

chematic of airlift development and pumping apparatus S (North Dakota State University, Scherer, 2005)..............................99

Figure 4.7

J etting system schematic (North Dakota State University Extension, Scherer, 2005).............................................................. 101

Figure 4.8 J etting heads (North Dakota State University Extension, Scherer, 2005)................................................................................ 101 Figure 4.9

irlift testing and development, test drilling in carbonate A aquifer (Ohio). The illustrated system is set up to permit periodic flow testing by measuring tank fill volume over a set period of time................................................................................ 103

Figure 4.10 T esting for field parameters during test drilling. pH, conductivity, temperature, and several key chemical parameters were measured in nonfiltered and filtered samples.... 103 Figure 4.11 Well pump electrical system protection (photo by Gary L. Hix)...... 110 Figure 4.12 S chematic of suction flow control device (Eucastream SFCD design, Kabelwerk Eupen AG product literature, Eufor S.A., Eupen, Belgium)............................................................................ 111 Figure 4.13 S and separator for submersible pump installation (illustration courtesy of LAKOS Separators and Filtration Systems)............... 112 Figure 4.14 B low-off hydrant examples (photos courtesy of Kupferle Foundry Company, illustration modified)..................................... 115


xvii

Figure 4.15 Example easy-to-service well house............................................. 116 Figure 5.1

Well decision-making flowchart................................................... 120

Figure 5.2

ome indications that you may have biocorrosion problems in S the well (Ohio). Corrosion hole (middle section, top), above pump was losing several 100 gpm................................................. 131

Figure 5.3

own- and side-view borehole video camera system operated D by Geoscope Inc., Mansfield, Ohio............................................... 132

Figure 5.4

xample pump performance curve (Scherer, 1993, AE-1057, E North Dakota State University Extension). Note: HP and head are per stage.................................................................................. 133

Figure 5.5 A plot of step-drawdown test data................................................. 134 Figure 5.6 A nalysis of step-drawdown test using Hantush-Bierschenk straight-line method, B established by intercept and C from slope of plot................................................................................... 134 Figure 5.7

raph of efficiency vs. pumping rate from analysis of step G test plot, aquifer loss and well loss illustrated............................... 135

Figure 5.8

lot of percent well efficiency vs. pumping rate. Derived from P analysis illustrated in Figures 5.5 and 5.6, with extrapolations to gpm above and below the tested flow rates (Figure 5.5)........... 136

Figure 5.9

ART method tube schematic. (Courtesy Droycon B Bioconcepts Inc.)........................................................................... 147

Figure 5.10 A selection of BART reactions from an alluvial aquifer well....... 148 Figure 5.11 I noculated BRS-MAG tubes and syringe applicator. Sample is injected into vial........................................................................ 149 Figure 5.12 W ellhead flow cell collector: (a) element and (b) as installed on a wellhead................................................................................. 153 Figure 5.13 E lectron micrographs (EMGs) of filamentous biofilms (Bureau of Reclamation project—scanning EMGs by L. Tuhela-Reuning, Ohio Wesleyan University)................................ 154 Figure 5.14 F ield analysis of drive cores for physicochemical and biochemical parameters (Iowa)..................................................... 155 Figure 6.1

Well maintenance decision tree..................................................... 172

Figure 6.2

rojections of annual and cumulative costs over time using P Sutherland et al. method. “Discounted annual costs” illustrates annual-cost profile, “Cumulative discounted costs” shows difference between “with” and “without” maintenance monitoring in this simulation............................................................191

xviii


Figure 7.1

ell rehabilitation work in motion. Cleaning carbonate W aquifer wells in western Ohio........................................................ 198

Figure 7.2

ometimes there are access challenges (photo courtesy of S Ohio EPA Southeast District staff)...............................................206

Figure 7.3

ood well site access is important. Note room for crane and G service vehicles on pad within fence, personnel access at the crane side to the interior and access through the roof...................207

Figure 7.4

ellhead in East Africa where site security is paramount. W Well service will require removing a portion of the “castle” wall................................................................................................207

Figure 7.5

ining a well, sealing off undersirable zones using a Griffitts L well packer (illustration courtesy Griffitts Drilling and Seals)..... 221

Figure 7.6

etting a liner in place using an inflatable swaging system S (illustration courtesy of Inflatable Packers International Pty Ltd).......................................................................................... 222

Figure 7.7

ireline or “riserless” pump installation schematic W (illustration courtesy of Inflatable Packers International Pty Ltd). A riserless pump uses the casing as the discharge line........ 223

Figure 7.8

FCD retrofit in well changes hydraulic profile (Eucastream S SFCD design, Kabelwerk Eupen AG product literature, Eufor S.A., Eupen, Belgium)...................................................................224

Figure 8.1

etting a well shooting charge (eastern Ohio sandstone-shale S well)............................................................................................... 234

Figure 8.2 S onar-Jet treatment sequence (Michigan). (a) The string is assembled and connected, (b) the assembled 5-ft string to be lowered to the screen interal, (c) the returning string after firing, (d) seeing what has been retrieved in the basket................ 235 Figure 8.3 A irShock air impulse gun. (Courtesy ProWell Technolgoies, Ltd.)............................................................................................... 237 Figure 8.4 A irburst AIG well assembly—bolt air gun mounted on bail (foreground), compressor and winches background...................... 238 Figure 8.5 A irburst treatment sequence (carbonate aquifer, northern Ohio). (a) Hooking up and deploying the tool, (b) checking water level, (c) inserting the tool, (d) visible results at the surface...........................................................................................240 Figure 8.6 p H influence on relative occurrence of hypochlorite ion species plotted from calculated data. Note that actual values may vary due to water quality and temperature variables............ 250


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Figure 8.7 I llustration of features of flexible well pump discharge pipe. (a) Coil of 6-in. pipe with fittings, (b) top connection at flanged well head, (c) pump connection, same installation, (d) full installation view, (e) installation of Wellmaster in an angled well (UK). Note that the pumps illustrated are not small. (Photos (b) and (c) courtesy of Boreline (Hose Solutions Inc., www.allhoses.com). Photos (a), (d), and (e) courtesy of Angus Flexible Pipelines.).......................................... 259

Disclaimer This work provides insight and understanding on the problems of wells and their prevention and cures and is presented as a reference work. It is not a detailed specification or substitute for experience. Any conclusions and recommendations provided are based on the informed professional opinion of the authors, and these are based on their experience and research. People just reading this or any combination of books and manuals should not consider themselves fully qualified to perform, specify, or supervise well maintenance and monitoring programs without the necessary knowledge base and experience with specific situations. Generally this knowledge and experience is concentrated in consultants and contractors, but there is no reason that it cannot be developed “in house” within a facility’s operations and maintenance staff. This book is based on a body of knowledge. How you apply it is up to you. The construction of wells is so individual and the geological environment so variable that we cannot guarantee the applicability or outcome in your particular situation. Also keep in mind that some of the procedures and technology mentioned are protected by patent. If you are a consumer of professional services in well rehabilitation, this book will help you to get the most from your professional help. A major point in this work is the need for operational data collection and maintenance. This is important. If you will not do this, we cannot help you with this book. If you are a provider, this book is a source of information intended to help you do your job better and more safely. With that in mind, and understanding that we all have a lot to learn, read on. Stuart A. Smith, CGWP Allen E. Comeskey, CPG

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Preface This book is intended to be a guide in keeping well systems operating to their best capacity. These include pumping water supply and plume control, pressure relief and dewatering wells, barrier and other recharge wells—horizontal, angled, and vertical. To a certain degree, the scope covers monitoring wells and drains, and even wells for hydrocarbon withdrawal and fluid injection. It is written for those people who have to wrestle with these problems: well and overall facility managers, their operators, consultants and regulators, and contractors who may perform well and pump repair and rehabilitation services. The problems you may be experiencing with your wells are not new or unique. They may be more intense for some wells than others. Each category of wells has its particular issues, for example: • Public water supply (PWS) and hydrocarbon wells are perhaps best covered by well maintenance and rehabilitation experience (since some are willing to spend money on it). • Private or farm water supply, small facility PWS, and some irrigation wells are also similar to other PWS wells, but often smaller in dimension and rarely maintained properly. • Monitoring and recovery wells are only specialized wells, but often installed where no reasonable person would put a water supply well unless they were desperate. • Recovery and treatment systems are also nothing more than specialized ground-water-source water treatment systems. What sets them apart from a maintenance standpoint is that they are routinely exposed to harsh environments and operated in such a way that maximizes the potential for performance and water quality deterioration. • Even where ground water is considered to be uncontaminated but monitored due to potential hazards, monitoring wells are subject to greater deterioration effects than active pumped water supply wells, since they sit for long periods, unused. • Aquifer storage and recovery (ASR) wells are increasingly being installed and used as utilities and regions attempt to better manage water resources. These systems are basically injection wells that can then be reversed to pumping wells. Injection wells have known maintenance problems. Can such wells be relied upon in the long run? • Increasing numbers of nontraditional nonvertical wells, like drains, have their own maintenance issues, exacerbated by the environments in which they are developed and by construction and development methods that leave them vulnerable to clogging mechanisms. xxiii

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The process of operating any engineered system should include active maintenance. The alternative (in this case, the neglect of well and pump problems) leads to continued performance deficiencies, or even additional problems. For a variety of reasons, wells have traditionally not been maintained like the active, valuable facility assets they are. However, an attitude of maintenance is catching on in all sectors. This current work is an update and expansion of the 1995 work, Monitoring and Remediation Wells: Problem Prevention, Maintenance and Rehabilitation, by Stuart Smith (CRC Press). That work was intended to accompany reports coauthored by Smith and published by the AWWA Research Foundation, Methods for Monitoring Iron and Manganese Biofouling in Water Supply Wells (1992) and Evaluation and Restoration of Water Supply Wells (1993), which were oriented toward water supply wells. These have now been out of print for several years (although they are still quite relevant). This present work reflects those changes and positive improvements in the state of the art that have occurred in the last decade or so. It builds upon and complements other titles in the Sustainable Well Series that have documented improvements in the last twenty years. This book, rather than focusing on one sector of well use as the 1995 book did, is intended to serve as a comprehensive yet readable state-of-the-art summary of performance maintenance, problem prevention, and rehabilitation or restoration practice for wells for the purpose of sustaining optimal performance over the long term. The current understanding of processes that impair performance and shorten well component life, practices designed to sustain performance during operations, and feasible rehabilitation and restoration methods will be considered. It will address design features to maximize sustainability and issues of cost-effectiveness in planning sustainable well efforts. Emphasis will be on operational practicality. It is a guidebook to the causes of well deterioration, methods of well maintenance, and well restoration or well rehabilitation methods. Like a useful travel guidebook, this work is not a one-stop encyclopedia, but, where useful, it points you to further sources of more information. In this case, the information for this work is built on the experience of the authors and numerous other people, and a good chunk of that information is published and should be on the bookshelf of—and read by—anyone responsible for well systems. We supply a recommended reading list. You know, as soon as you stop and go to print with a book, that a good story will come your way or a new technology will emerge that may sweep the industry. So consider this book as a snapshot. By all means, keep up with new developments. Even with new technology, most of the principles expressed herein will apply. Seek all the good advice you can find, and respect it when you get it. The coauthors offer a website for up-to-date information, and they link it to other good sources. We plan to offer a discussion blog or some such vehicle for those who purchase the book in order to update the reader on new findings and ideas and to access additional resources.

Preface

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A Comment on the “Voice” of This Book The authors have devoted much time in front of groups of operators, municipal boards, etc., informing them of the mysterious goings-on in their wells. We have found that a relaxed discussion results in more understanding than a formal lecture. While the material is intended to be entirely serious and authoritative, we have applied the same style to this book. We envision ourselves sitting on our stools, talking with you. As with instruction, we repeat ourselves at times for emphasis, in case your attention drifts.

Authors Stuart A. Smith has been managing partner of Smith-Comeskey Ground Water Science LLC (Ground Water Science) since 1996. He is certified (CGWP) and licensed as a hydrogeologist and is a highly applied environmental microbiologist focusing on the biofouling and biocorrosion issues of wells and geotechnical drains. Prior to forming the predecessor of Ground Water Science in 1986, Mr. Smith served as a technical editor for Battelle Memorial Institute, as an adjunct associate professor in ground-water technology for Wright State University (Ohio), and as education program coordinator and research associate for the National Ground Water Association (NGWA, then known as the National Water Well Association), where he joined the staff in 1979 after a short stint as a secondary school teacher in Ohio. He also served as a lecturer in biology at Ohio Northern University in the 1990s. He holds BA and MS degrees from Wittenberg University (Ohio) and The Ohio State University, respectively. He is the author or coauthor of numerous publications, such as Methods for Monitoring Iron and Manganese Biofouling in Water Supply Wells and Evaluation and Restoration of Water Supply Wells (AWWA Research Foundation), Monitoring and Remediation Wells: Problem Prevention, Maintenance and Rehabilitation (CRC Lewis Publishers), and Operation and Maintenance of Extraction and Injection Wells at HTRW Sites (U.S. Army Corps of Engineers), and the first manual on the subject in Spanish (with the late Dr. Miguel Gariboglio), Corrosión e incrustación microbiológia en sistemas de captación y conducción de agua: aspectos teóricos y aplicados. He is also a contributor to AWWA’s Water Quality & Treatment, 5th edition and ASCE’s upcoming International Manual of Well Hydraulics (ASCE). He is a coauthor of both the 1992 Australian Drilling Manual and its 1997 successor, Drilling, published by CRC Press, and principal author-editor of NGWA’s 2nd edition of the Manual of Water Well Construction Processes. Since 1980, he has contributed to the general understanding of causes and cures for well problems through talks and seminars across North America and in Argentina and Australia, and through industry publications, such as the Water Well Journal and National Drillers Buyers Guide/National Driller, and web content. He is active with the NGWA (including being active in the development of the new water well standard, ANSI/NGWA-01) and the AWWA’s Ohio Section. He is currently chair of the Standard Methods for the Examination of Water and Wastewater joint technical group for Section 9240 (iron and sulfur bacteria). He is also active locally with the Sandusky River (Ohio) Watershed Coalition and involved in some water supply development planning in East Africa. Allen E. Comeskey has been a member and partner in Ground Water Science since 1996. He is a certified professional geologist (CPG) and registered geologist in several states. He has been involved in water supply hydrogeology and exploration since 1979. With Ground Water Science, he focuses on well construction planning and xxvii

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execution, and the performance and analysis of logging and well hydraulic and aquifer tests. He is also an experienced ground-water modeler and hydrologic analyst with extensive experience in both fractured rock and glacial-alluvial hydrology. Prior to forming Ground Water Science, he worked for 10 years with the North Dakota State Water Commission, and also with Earth Data and LBG, Inc. on projects in Maryland, New York, Pennsylvania, and New England. While in North Dakota, he conducted community and county water resources exploration and delineations (often logging more than 50,000 ft of borehole each year), and worked with wetlands water budgets. While in the eastern United States, he worked on complex wellhead protection and contaminant delineation studies and continued detailed modeling, well testing, and well rehabilitation project work with Smith-Comeskey. He holds BS and MS degrees in geology from Bowling Green State University and the University of North Dakota, respectively, and has completed advanced study in fractured rock hydrology and modeling at the University of Wisconsin–Madison and GIS at BGSU.

Acknowledgments Thanks to the past support of AWWARF (Water Research Foundation) at that crucial time in the early 1990s when good information was being compiled again. They can fund future needed research proposals we send if they want to. Thanks also to the U.S. Army Corps of Engineers (USACE), the U.S. Department of Interior’s Bureau of Reclamation (BOR), and the National Ground Water Association for past and present support and confidence. “Up north,” Canada Agriculture’s Prairie Farm Rehabilitation Administration (PFRA) and the private company Droycon Bioconcepts, Inc. have provided vision, leadership, and crucial support to the art, and those witty Canadians coined the catchy concept of a “sustainable well.” We also acknowledge other working experts and authors in the field, who help one another learn and improve “as iron sharpens iron” (even in those instances when we do not agree). The input of George Alford, Olli Tuovinen, Roy Cullimore, Bill Frazier, Gennady Carmi, Miguel Gariboglio, Jay Lehr, Ross Carruthers, Rob McLaughlan, Peter Howsam, John Schneiders, Denise Hosler, and many others over the years is particularly appreciated. We most gratefully thank our clients who had the problems that have served as our classroom and laboratory (we benefit from the troubles of others), as well as our working colleagues on the service side, who move the iron and the water. Nothing gets done without them. Karen Ward helped with art carried over from the 1995 predecessor to this work. We slavishly acknowledge the support of our wives, who mostly humor us as we pursue our star. Crack librarian Rebecca Quintus, who finds things we seek, also contributed materially to this work.

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Colorful History 1 AofBrief Well Maintenance and Rehabilitation and Their Milestones 1.1 Some History No one recorded when well digging started, but surely humans imitated elephants in digging holes in the sand to access cooler water that did not make the children sick so quickly (Figure 1.1). People dig such “wells” to this day. Well construction is an ancient craft: Genesis, the book of the Judeo-Christian scriptures that provides an account of the primordial history of human interaction with God, recounts the exploits of Abraham, leader of a large and successful nomadic pastoral clan and claimed as patriarch by many, living about four thousand years ago. Operating in a semiarid country, Abraham’s company (like their neighbors) dug wells, a skill they learned from other people in the Levant who had already been constructing wells for several thousand years. Excavated wells in Europe, Syria, Israel (including a site now 10 m deep in the sea), and South Asia have been dated to before 6300 BCE. As for the subsea well, people presumably constructed wells on land to access fresh water, so the well was constructed before the sea level rebound at the end of the last Pleistocene ice advance. Since such wells were valuable (Genesis reports squabbling among the tribes over Abraham’s wells), there presumably has been well maintenance and rehabilitation since that time—and before—if you count all that sand, silt, and debris removal from all those countless wells in dry riverbeds back to the dawn of humanity. Maintenance must have been at least selectively successful. In Jesus’ encounter with a woman at a well in Samaria (early first century CE), she attributes the source of the well to the patriarch Abraham’s son Jacob (who lived over seventeen hundred years before). That’s some long well life. Naturally, maintenance of dug wells was not always performed, or performed well. Excavated wells are excellent sources of archaeological information from old settlements such as colonial sites in Virginia, Jamestown or Williamsburg. Objects in wells mean that people were throwing undesirable objects into wells back then, just as they do today. One of us (Comeskey) observed in North Dakota in the early 1980s (a process since stopped) that wherever a platform over an old dug well rotted away, the hole was soon filled with pesticide jugs and oil cans. As we see everywhere, if there is a hole in the ground, someone throws something in it. 1

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Sustainable Wells: Maintenance, Problem Prevention, and Rehabilitation

Figure 1.1 Elephant digging for water in sand. (Tarangire National Park, Tanzania)

Objects Found in a 400-Year-Old Well at Jamestown, Virginia Plants, wild and domestic seeds, pollen, parasites, insects, paper, leather, pewter, wood, ceramics, beads, fabric and other materials and food remains (a great quantity of butchered animal bones, oyster shells, and other marine life, including clam, mussel, and scallop shells, fish bones, dorsal plates from huge Atlantic sturgeon, crab claws, and barnacles). historicjamestowne.org Likewise, spoiling wells is an ancient tactic in warfare that was applied as recently as the Balkan wars and Rwandan civil strife of the 1990s, when human remains were dumped in wells. With less intention, spoiled wells can change history. Black rat remains found in Roman wells in Britain suggest that Romans may have lost their grip on northern Europe due to bubonic plague. When such wells required attention, there was no simple option to “move over and drill new,” especially in rock country. Establishing a new well would involve an incredible investment of labor, since the engine-powered drill would not appear until the nineteenth century. Cleaning the existing well would be the more cost-effective strategy in terms of time and labor, even if it were risky.

A Brief History of Well Maintenance, Rehabilitation and Their Milestones

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Georg Houben and Christoph Treskatis, in their excellent McGraw-Hill book (see the recommended reading list), recount examples of well maintenance and reconstruction dating back to Neolithic times. One notable example of premodern well maintenance comes from Germany. By the sixteenth century, regular well maintenance on two- or three-year intervals was established in the city of Duderstadt. This took the form of a “well-cleaning feast.” Sadly, they report that the practice was abolished by 1724 “because the amounts of beer (5 barrels) served—free of charge—during this festivity caused ‘… on the one hand much exuberance, fighting and desecration of the holy days, on the other hand also the ruin of citizens and neighbours….’” Maybe this is why we have industrial safety regulations today, but it must have been more fun then. Well maintenance and rehabilitation through the history of dug-masonry wells was largely limited to cleaning out debris and silt, cleaning off what we would now call biofouling, and necessary deepening and reconstruction. The use of chlorine (chlorinated lime) as a disinfectant began in the nineteenth century in response to disease outbreaks associated with wells. One widely reported account is that of Dr. John Snow’s attempt to disinfect the Broad Street Pump in London in 1850 during the cholera outbreak, which Snow pinned on that infamous well. That it would occur to anyone to disinfect a well, of course, required an understanding of germ theory, which also did not emerge until the nineteenth century, and the industrial extraction of chlorine, also an innovation of the 1800s. The face of well construction changed dramatically in the nineteenth century in Europe and the Americas with the advent of the steam engine and engine-powered reciprocating drilling machines. Although Chinese drillers reportedly drilled 1,000 m salt wells four thousand years ago with spring pole drilling systems, these took generations to complete (as one can imagine) and were therefore rare and valuable. The appearance of the steam engine attached to a drilling machine (dated to the 1830s in the United States) provided a reasonable means to drill deep wells into aquifers rarely tapped before. These were better protected from contamination and tapped water with more abundant reduced iron, manganese, and sulfur. Although more sanitary and easier to protect, their inefficient water intakes were more vulnerable to clogging by what we would come to know as iron, manganese, and sulfur biofouling. Thus, we came to an approximation of the modern drilled (tube) well maintenance situation:

1. A productive and valuable well that was (to varying degrees) prone to performance, sanitation, and structural issues. 2. The well is now deep—often quite deep—but no longer accessible for direct action by masons or youth with brushes and buckets. 3. Yet on the other hand, it could be built using engineering, process, and chemical capabilities also unavailable in previous millennia. For example, it can be pumped using a wind- or engine-powered piston pump.

The early decades of the twentieth century brought these notable advances in water well science, engineering, and technology:

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1. The emergence of the cable tool drilling machine and associated tools and methods in their modern form provided a viable, powerful, and versatile well construction and service system 2. Modern well screen designs and other inventions with familiar names attached to them, such as Johnson, Layne, Moss, and (not to be forgotten) Cook 3. Modern metallurgy, giving us high-strength and corrosion-resistant alloys, precision machining, welding, and other fabrication methods 4. Development of technical procedures such as well grouting and filter packing 5. Development and adoption of the vertical turbine pump 6. Electric line power (often of high quality) becomes widely available 7. Development of well testing and analytical methods that are still in use today

As such drilled wells accumulated some age, performance decline and a need for rehabilitation, and of course pump service, became inevitable. As long as there have been well development tools and procedures, mechanical redevelopment has been used to clean wells that had filled with sediment or declined in performance. For many purposes, redevelopment worked well. However, it was not long before people tried various means to enhance the experience. While talking with a retired driller, Hubert Keith, in the early 1980s, he related to one of us (Smith) that Layne Mishiwaka crews in the 1930s pumped hot water and steam generated by their steam-powered cable tool rigs into wells to dislodge “iron bacteria” deposits. They would let the wells work and pass the time reforging drilling bits. This is the kind of patience (rarely expressed today) that Depression-era men, glad to have good jobs, possessed. Houben and Treskatis report that a Heinrich Böttcher filed a 1905 patent in Germany (no. 181,578) that dealt with the “cleaning of tube wells by means of hot steam.” So the concept had widespread application. The post–World War II period brought more revolution. The first was the spread of the truck-mounted rotary drilling rig. While they were used before the war, especially in the petroleum field, they were slow to be adopted by the water well industry due to cost and their complicated nature. However, once they became economical to deploy (and there was a suburban housing market), rotaries became common. Wells could be installed very quickly and less expensively. There was much less investment in time and emotion compared to installing them with cable tool rigs or by digging. Consequently, wells became consumables, to be used and discarded. Why maintain something you are going to use up and replace? In 1955, we had cheap land, cheap drilling, and limited regulatory environment. A second revolution was in the flowering of industrial chemistry, which made a wide range of cleaning and disinfecting compound chemicals available for use in well cleaning, and the ingenious experimented with a lot of them. Mineral acids such as hydrochloric acid were used for removing deposits. Chlorinated lime, chlorine gas, and liquid sodium hypochlorite were used for disinfection and odor removal. The use of chemicals became more prevalent after World War II, with the final passing of steam engines and the universal use of internal combustion engines to power drilling equipment. The proliferation of designer organic chemicals after World War II brought us the age of detergents, beginning in the 1950s. Paging through water well industry


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journals of the time, one finds wide-eyed articles and advertisements for compounds from familiar manufacturers. These phosphate-containing detergents were a major part of the well-cleaning toolkit for decades. Starting in the 1980s, more sophisticated chemistry that presented fewer side effect problems came into wider use. The period since the early 1980s brought a modern flowering of research, conferences, and publications (especially since the early 1990s) on well rehabilitation and maintenance. There was much experimentation in types of processes. That same period brought some of the first systematic experimentation and training in what constitutes effective well cleaning and maintenance. It also brought the era of well cleaning mass marketing, in which companies (including some of the major suppliers in the ground-water industry) provide us with designer compounds intended to be better and safer than what we select a la carte off the chemical supplier’s dock. Many of these products have names with letters and numbers. The innovation, testing, and exuberant marketing continue to the present day.

1.2 The Role of the “Environmental” Sector in Shaping Well Rehabilitation and Maintenance Millions of wells have been constructed in the industrialized world, mostly since the early 1980s, for a purpose other than the traditional ones: ground-water supply, recharge, or dewatering. Among these other purposes are monitoring ground-water quality and pumping to control or clean up contaminated ground water—the other side of the effect of the industrial chemical era on the industry. At the same time that construction of such environmental wells was accelerating, the environmental industry (consultants, government, drillers, and service users such as waste management firms), one challenge was to make remediation systems work in an environment far more challenging than that of a potable ground-water system. The development of several important consensus standards, including ASTM standards for construction and development and maintenance of monitoring wells, helped the process. An entire training and continuing education industry sprang up to service the needs of professionals in the environmental industry so that monitoring and recovery systems could be competently designed and installed. Manuals on monitoring well construction and design were written. Improved methods, tools and equipment, and personnel skills were developed and became part of the maturing of the industry. The results are not uniform—poorly designed systems are not disappearing. Unfortunately, with the gutting of funding for ground-water clean up, much of the training and continuing education sector has withered, but the publications and concepts remain. The remediation side of the business has been transformed since the mid-1990s with the phasing out of many pump-and-treat systems due to their high operational failure rate. It is not that such systems could not be maintained, but resources and plans to do so were rarely included in project plans. The entire budget went to design and construction. In their place, in situ remediation has been a more prevalent tactic. Of course, the whole pace of ground-water cleanup slowed in recent years with the loss of funding.

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Figure 1.2 (See color insert following page 66.) Pump impellers clogged by oxidized iron deposition. Extraction well, DOE Fernald Preserve (Ohio).

In recovery and pump-and-treat systems, the chief problems are reduced flow and increased drawdown in the well systems and clogging of downstream piping and treatment apparatus. Pumps are a particularly hard-hit component of the system (Figure 1.2). Environmental well problems are fundamentally the same as those that cause water supply wells to provide poor performance. Poor design and poor construction and development also can contribute. However, inherent environmental causes of deterioration may occur even if design, installation, and development are adequate. Note: We use numerous technical terms such as drawdown throughout this work. We are assuming an audience generally familiar with wells and their processes. If you are entirely new to well construction, testing, etc., we suggest reviewing primers on the subject (and do not forget to read the disclaimer and other warnings in this text). Monitoring wells may have less obvious performance symptoms since they are not always stressed by pumping. Symptoms of well deterioration experienced in monitoring wells are most likely to include changes in physicochemical water quality and increased turbidity. Such changes can interfere with the quality of samples from wells, as well as their performance, for example, interfering with the recovery of organic constituents of ground water such as trichlorethylene (TCE) results in erratic sample results over time. Results become more consistent after wells are rehabilitated. Aquifer storage and recovery (ASR) wells represent a new development in terms of their being in mainstream use. Injection wells for management of coastal salt water intrusion and barrier wells are known to be prone to particulate and biological clogging (Chapter 2). Such wells and associated infrastructure are large investments based on rather meager research into longevity issues.

1.3 The Impact of Biology on Hydrogeology and Ground-Water Technology Much to the bafflement and annoyance of many people with pure physical science and engineering backgrounds (not everyone certainly), the concept that biological


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occurrence, activity, and functions have significant impact on or dominance over the behavior of water and water constituents in the subsurface and the performance and service life of our engineered structures in the subsurface has become more and more difficult to ignore. Everything about planet Earth, from the stratosphere of the atmosphere down to the base of the crust, is affected by life, and has been profoundly transformed since life appeared on Earth. Microflora are ubiquitous. If there is a niche, they exploit it. If there is a pore space, they occupy it. If there is a surface, they coat it. The world as we know it is a product of the actions of living things. This revolution in understanding is hardly new. A very good conceptual understanding of the role of microflora in what we now call geomicrobiology (a term coined by 1954, according to Ehrlich (see Ehrlich and Newman in our recommended reading list)) developed in the late nineteenth century, but went quiet for several decades for historical-political reasons. “Geomicrobiology” pioneers were Russians, and the Soviet revolution came along in 1917. By the 1950s, a revival of interest was developing in some academic circles. H. L. Ehrlich’s first edition of Geomicrobiology appeared in the 1960s. The field gained traction by the 1970s in various research groups and at the U.S. Geological Survey. A lot of good work continued to be published in Russian (largely inaccessible to Americans). Finnish geochemists and environmental microbiologists (who read Russian and German and communicated well across the Iron Curtain) were among the leaders in the “breakout” in the 1970s and 1980s. Diffusion of these concepts to the practical ground-water field was rather slow. One of us (Smith) was the only individual on the staff of what was then the National Water Well Association (now National Ground Water Association) with a biology degree in the early 1980s. So he fielded all the inquiries about biological things and started on his “life of slime.” He met a lot of resistance and doubt when speaking about microbial corrosion and clogging. By the publishing of this work’s predecessor, Monitoring and Remediation Wells: Problem Prevention, Maintenance and Rehabilitation (CRC Press) in 1995, the role of microbial activity in well problems and the remediation of contaminated ground water were well on their way to being accepted in ground-water development and environmental remediation circles. By then, the now well-known Biological Activity Reaction Test (BART) tests were in the market and tested, a lot of work had been done in cleaning biofouled wells, the U.S. Department of Energy supported landmark work in deep subsurface microbiology that was very revealing, and D. R. Cullimore’s first edition of Practical Manual of Groundwater Microbiology was published by CRC Press. This growth and development (and intellectual acceptance) of the role of life in the ground-water engineering world has continued. Such a paradigm shift in thinking is consistent with the growing acceptance of the idea of an integrated, interactive universe and intedisciplinary study of phenomena. Although geomicrobiology has been experiencing another academic revival due to interest in global climate change and the possibility of life on Mars, the academic activity is not translating well into applied practice. It seems like a lot of people still are not paying attention. Ground-water remediation systems, especially those for commercial properties, are designed as if biological clogging will not occur— even if the system is designed to foster bioremediation. Then folks are stunned

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when clogging does occur, but they remain unwilling to take the necessary steps in response, expecting it to simply go away or to be treated cheaply. A more subtle issue is that of the influence of developed biomass on well and aquifer hydrology. Actually, the physics and math are what they are. If a biomass clog is present, it lowers the hydraulic conductivity and alters flow paths, so the effects of biomass development can be analyzed and modeled with available tools. The weakness in hydrologic practice is the persistant assumption that the water level response of pumping and monitoring wells (regardless of age and condition) during tests transparently reflects the surrounding aquifer. Experience shows that is not the case. We even have math for that: analysis of “skin effect.” The problem with taking well biomass development into consideration is that to do so requires an initial step of well reconnaisance to assess conditions and then factoring those conditions into the analysis in a meaningful way. This requires a budget for such work, and suddenly, everyone likes simplifying assumptions. Myths like “isotropic and of infinite areal extent” are popular in the effort to do ground-water protection modeling on the cheap, for example.

1.4 Economics, Human Skills, Personalities, Demographics, and Other Issues As will be discussed further in this work, the economics of energy, land availability, water, and scarcity are driving a renewed interest in the economic benefits of well cleaning and maintenance in the commercial and municipal sectors. Practice is beginning to catch up with ideals, theory and persistent preaching. More of the water well industry has embraced rehabilitation, along with drilling, especially as the economic attractiveness of service has become evident. There is a beginning of a sense of economic value for ground water that was lacking before. Also, there is a sense that sustainable choices must be made: we cannot just run down a wellfield through neglect, then move over and establish another. There may be no other place available. Nontechnical human choices heavily influence the acceptance of ideas and technologies. The Enlightenment movement in Western thought led to a flowering of robust science, but the Enlightenment’s model of a mechanistic, clockwork universe results in resistance to ideas such as complex, literally organic interaction of formation materials, hydrology, biology, and operations. Interestingly enough, the “mechanic” side of the ground-water field, the water well contracting sector, embraced the biological clogging and corrosion model faster than their colleagues with academic and engineering credentials. This organic view of the situation fits their experience in life. Life is an integrated whole of earth, biology, machines, people, institutions, and various intangibles such as matters of faith. The modern story of water well construction, maintenance, and rehabilitation is also a social history, and heavily influenced by personalities.

1. It is impossible to envision the development of modern (meaning nineteenth century to present) water well and environmental technology without (a) free enterprise, (b) the American view of patent and intellectual rights


(inventors should benefit from their work, and this is something to shoot for), and (c) the development of oil and gas. People had incentive to invent, try new methods, and take risks because they could benefit materially. Otherwise, we stay in the feudal system. The water well and rehabilitation fields are rich with invention. This continues today. Oil required invention to make serious progress and money. Oil and gas were the drivers for the cable tool rig’s development, the blowout preventer, and the tricone drilling bit, among so much more. Oil is valuable and people have strong incentive to invent and engineer to get it. Face it—people will get water from a creek. It required an economic incentive (irrigation, settling on prairie land, raising living standards) and social imperative (improve the lives of the poor and women) to drive improvement in water. 2. We have to make note of the “farm boy” phenomenon of North American society (which includes “farm girls” by the way). University engineering departments recognize that farm kids make the best mechanical engineers. Whether or not they have an engineering degree, people with this rural, machine-rich background know how to figure out how things work and how to do things like making field innovations and repairs. Are we losing this capacity-building ability in our society? 3. The story is full of colorful and interesting individuals. The 2007 movie There Will Be Blood, based loosely on Upton Sinclair’s 1927 novel Oil!, follows one such character, an inventive sociopath. That example is rather extreme. The pioneers and current drivers of the ground-water industry, especially the water well sector, are not likely to commit child abandonment and brutal acts of murder, but they tend to be individualistic, creative, technically focused inventors. They are not organization people. The drivers of recent improvements in well cleaning practice include the pioneers and visionaries typical of new or newly flowered technologies. It is impossible for us to imagine the current state of well diagnosis, maintenance, and cleaning without several people who demonstrated laserlike focus on these subjects—personal mission, actually, that resembles some kind of apostolic calling more than personal choice. Two that come to mind are the late George Alford on the cleaning side and his collaborator, Roy Cullimore (and his longtime devoted staff of associates). Then there is the skill of tent preaching that brings the sinners to repentance and salvation: Where would we be without Dave Hanson in that regard (setting aside for the moment some details of doctrine)? One person who labored in relative obscurity, and who should not be forgotten, is the late Miguel Gariboglio of Argentina. Since most of the publication in our field is done in North America and Europe, and much of it in English or its technical cousins German and French, this Spanish-speaking Argentine labored off on stage right. Besides, during the height of his work, Argentina was economically and politically isolated. Still, he and a number of his compatriot colleagues labored on developing and practicing practical biofouling and biocorrosion diagnosis in a very difficult situation, adding materially to our knowledge.

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4. However, despite how we lift up and remember the colorful personalities and the pioneers, the full mainstreaming of well cleaning required the influence of our “mud” and “screen” company colleagues. These businesses put the “soap” in jugs on the shelf with the appropriate instructions and certification labels, print the literature, staff the booths, and generally have brought well cleaning to the back roads of North America. Likewise, our laboratory supply mass marketers, with their catalogs and websites, and using our relentlessly organized package transport system, put the new biological tests in the hands of the operators who need them. Together, these businesses generally brought the combination of mass marketing and relentlessly efficient distribution that has come to be known as “walmarting” to well maintenance and cleaning tasks. 5. The occurrence of a maintenance mindset: The worldview that it is virtuous and valuable to maintain valuable systems is one that is culturally dependent and somewhat dependent on economics and other intangibles. Indoctrination is important (as we will discuss). One also finds that the maintenance ethic is most evident in societies (and segments of those societies) that have the most experience with machines and complex engineered structures (e.g., agriculture). This ethic is magnified when one owns or has fiduciary responsibility for the object of maintenance. Maintenance vision can be selective. This is well exemplified by the experience of water wells. People are most likely to maintain what they see or can otherwise readily detect. Operators will maintain a pump (especially a lineshaft turbine) but neglect the well structure. A maintenance ethic is less evident in societies (such as in the developing world) where machines have been dropped in by outsiders rather recently without transition from a previous condition. A state of lack of maintenance is amplified when the local people do not own the asset. Then the donor gets the message, “Dear friend, YOUR [fill in the blank—tractor, well pump, etc.] is broken. Please send money.” When frustrated by such a situation, understand that experience and comfort with (even love of) machines and systems comes through generations of acclimation and familiarity. Remember that the current state of ground-water technology had evolved over close to two centuries by the time this work was written. Such lapses of maintenance vision and planning occur in the United States. Here, funding for maintenance (as we discuss later) is not universally provided. Under some urban areas, subways were constructed, and in some cases, operated for some time but left to deteriorate due to lack of maintenance, and then abandoned. Highways and other infrastructure are often built, funded by grants, without maintenance funding and requirements. The political system can generate the will and momentum to build it, but no long-term commitment to maintain it. The rise of the “asset management” culture from roughly the turn of the twenty-first century is an attempt to systematize asset maintenance and financial responsibility. This is a system and ethic that can be readily (and rightly) applied to the specific assets known as wells and associated systems.


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6. The deep training, indoctrination, and knowledge needed to do these properly are yet to be mainstreamed. There is much evidence that many in charge of operating or advising operators of ground-water assets have paid no attention to the last twenty years’ progress. We (the authors) provide training where we can, as do some others. This book is one attempt to extend our reach. Fortunately, well cleaning methods now being lifted up (as described within) are relatively effective and much less hazardous than older methods, even if applied inefficiently. Just when improved well cleaning technologies are being mainstreamed, we now are experiencing a relative shortage of the service personnel necessary to perform well service work. As in the water and wastewater operations sector, the skilled and available ground-water industry workforce in the United States is aging. It remains predominantly rural, white, and male, while the United States is increasingly urban and pluralistic. Language and (sometimes ridiculous) immigration barriers impede the recruitment of other willing, skilled workers, and many women with the right skills and temperment find better pay and working conditions in other sectors, such as medical trades. Many other good people for this work are also occupied with being in the military—indefinitely it seems. How this will work out will await future works.

1.5 A Word about Terminology Our English language (the only one either of us uses with any confidence) allows for subtle subdivisions of meaning and easy word creation. In the current context, the process of cleaning and repairing a well to improve or restore performance has been referred to as rehabilitation, remediation, restoration, and simply as well cleaning. Each has merit. Remediation is a term often reserved for cleaning up contaminated ground water. That is how we will use the term here. Restoration was used in Evaluation and Restoration of Water Supply Wells, the 1993 manual that one of us (Smith) coauthored. That is a good term, but it may be too optimistic. Cleaning is a straightforward concept, and we use it herein for the process of clearing out debris, biofouling, and so forth. It implies, but does not promise, restoration. Roy Cullimore, in the new edition of Practical Manual of Groundwater Microbiology, favors regeneration for excellent reasons, including facility manager distaste for rehabilitation, which reminds them of the process of bringing injured workers back to health—an uncertain process with hidden costs and legal minefields, as he points out. We choose to stay with rehabilitation because it is a widely understood and used term for what we are discussing, and the process does have those features: risk, uncertainty, and hidden costs. Thus, we promote preventive maintenance as a lower-risk and more sure policy alternative. Besides, we would have to conduct a word search and change a lot of text, and we are acquiring age-related attention-deficit disorder as we look ahead to more important struggles in life than word choices. As you read Cullimore’s work (and you should not fail to do so—order it now if you do not have it), you will find some other differences in terminology. We stay with biofilm and biofouling where we use them and use biomass less often, although

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he is entirely correct in his choices. We tend to stay with a much simplified and mainstream choice of terminology. As you applaud our choice, remember that his terminology (consortia, biomass, no iron bacteria, etc.) pushes into mainstream literature and teaching, displacing the “mainstream.” It will continue to do so as long as he is writing and people pay attention to what he says, for he is the prophet of biology in the underground and we are apostles, applying and proclaiming what is revealed to us. And finally, following decades of U.S. Geological Survey usage (through March 2009) and the preference of the National Ground Water Association, ground water is two words as a modified noun and hyphenated ground-water as an adjective. Either that or we go with surfacewater, drinkingwater, or potablewater in the German style. Enough pontificating, on with the meat of the discussion …

and Effects 2 Causes of Well Deterioration Well deterioration is a serious concern in the operation of ground-water systems. Causes include formation, water quality, and biofouling, as well as operational, factors. In order to understand and deal with well performance problems, it is necessary to understand causes of well deterioration and how they affect the performance of the well. Even if you now already have deteriorated wells and are looking for solutions, take some time to absorb this information.

2.1 Summary: Causes of Poor Performance There are numerous causes of poor and deteriorating well performance. Causes may include inherent characteristics of the formations that supply water to the well, well design and construction, and the ground-water quality. Operation of the well comes into play as well. Table 2.1 is a list of several categories of poor well performance or malfunction and likely causes. Chances are that several interacting factors are involved in your well’s problems. Think of these as interactive.

2.2 True Grit—Sand and Silt The infiltration of sand and other particulate fines remains one of the most common problems faced by well operators. Pumping sand and silt in the product water wears pump impellers and other components and clogs the downstream system (Figure 2.1). “Sanding” has a number of causes, including inadequate filtration design (large nonengineered slots and other engineering deficiencies, mobilization of fines in rock fractures, and breaks in sealing system components such as grout or casing). In some cases, high entrance velocities through engineered screens and gravel packs can cause sand pumping, usually when the filter pack fails to stabilize the aquifer and sand enters the well. These issues are exhaustively discussed in a wide array of available industry literature (see our recommended reading list) and do not need to be detailed here for the diligent student of well performance, although we taken them up as a topic of prevention in Chapter 4. Much of the same information is available online for the less motivated, and those who do not or cannot access the better references. Proper screen and filter pack design are adequately considered in the above-mentioned well construction publications and will not be detailed here, except to note that proper design practices, such as those spelled out in the National Ground Water Association’s (NGWA) new Water Well Construction Standard (ANSI NGWA-01), should be followed. 13

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Table 2.1 Categories of Well Problems and Related Causes Problems

Causes

Sand/silt pumping: Pump and equipment wear and plugging

Inadequate screen and filter pack selection or installation; incomplete development; screen corrosion; collapse of filter pack due to washout resulting from excessive filter pack vertical velocity; presence of sand or silt in fractures intercepted by well completed open-hole; incomplete casing bottom seat (casingscreen break) or casing-screen break due to settlement, ground movement, or poor installation; pumping in excess of gravel pack and system capacity (oversized pump, pipe breakage— lowering pumping head, etc.)

Silt/clay infiltration: Filter clogging; sample turbidity

Inadequate well casing seals; infiltration through filter pack or “mud seams” in rock; inadequate development; casing-screen break due to settlement, ground movement, or poor installation; formation material may be so fine that engineered solutions are inadequate

Pumping water level decline: Reduced yields; impaired pump performance; increased oxidation; well interference

Area or regional water level declines; pumping in excess of sustainable aquifer capacity; well interference; well plugging or encrustation; sometimes a regional decline will be exaggerated at a well due to plugging

Lower (or insufficient) yield: Unsatisfactory system performance

Dewatering or caving in of a major water-bearing zone; pump wear or malfunction; encrustation; plugging; corrosion and perforation of discharge lines; increased total dynamic head (TDH) in water delivery or treatment system

Complete loss of production: Failure of system

Most typically pump failure; also loss of well production due to dewatering, plugging, or collapse

Chemical encrustation: Increased drawdown; reduced output; reduced injection acceptance rate

Deposition of saturated dissolved solids, usually high Ca, Mg carbonate, and sulfate salts, or iron oxides or FeII sulfides; may occur at chemical feed points, e.g., feeding caustic soda to raise pH into a Ca-rich water

Biofouling plugging: Increased drawdown or reduced injection acceptance rate; reduced output; alteration of samples; clogging of filters and lines

Microbial oxidation and precipitation of Fe, Mn, and S (sometimes other redox-changing metals that are low solubility when oxidized) with associated growth and slime production; often associated with simultaneous chemical encrustation and corrosion; associated problem: well “filter effect”—samples and pumped water are not necessarily representative of the aquifer; often works simultaneously with other problems, such as silting

Pump/well corrosion: Loss of performance; sanding or turbidity

Natural aggressive water quality, including H2S, NaCl type waters, biofouling, and electrolysis due to stray currents; aggravated by poor engineered material selection

Well structural failure: Well loss and abandonment

Tectonic ground shifting; ground subsidence; failure of unsupported casing in caves or unstable rock due to poor grout support; casing or screen corrosion and collapse; casing insufficient; construction and service work and other local site operations

Causes and Effects of Well Deterioration

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Figure 2.1 Impellers destroyed by pumping sand and gravel (Mexico).

Recommendations on what is “proper design practice” vary somewhat (see also Chapter 4). Simplifying for conceptual purposes, the Western (U.S.) design school centered around the long gravel-packed louver screen accepts much higher slot entrance velocities than the wire-wound screen (e.g., Johnson Screens) design school. These differences in design follow differences in the hydrogeology-well-construction interactive system that they are designed around. This is important and proper: hydrogeologic parameters should drive well design, with parameters derived by thorough hydrogeologic testing and analysis. Some well design practices seem to assume that the earth can be forced to submit to the will of the engineer or regulatory authority. One trend in our experience is that of moving toward conservative slot selection to avoid sand infiltration. No one wants sand infiltration, but conservative slot selection can sacrifice efficiency and long-term performance to achieve that goal. The smaller the slot in any particular geochemical environment (see following), the sooner it will plug. If fines are going to be a problem, we advocate using a well-designed filter pack (following well-researched design practice) and budgeting for extended development. In the glacial-fluvial outwash valleys that are part of the experience in the Great Lakes region of the United States, we often encounter a wide and even bimodal distribution of particles in immature sediments: That is, the sieve analysis (including those obtained from Rotasonic cores) yields (1) boulders and (2) fine sand. Such a distribution is extraordinarily difficult to screen and prone to migration of fines toward the well, so designed filter packs are necessary. When an otherwise sensibly designed filter pack becomes partially or entirely plugged with fine-grained material, oxidation products, or biofouling (see following), the hydraulic conductivity of the filter pack is locally reduced, resulting in increased velocity and head losses through the filter pack, which increases the well loss component of total drawdown and can induce sand pumping. When near-screen velocities are too high in a well tapping a formation containing abundant fines (e.g., glaciofluvial aquifers), sand sealing by fines occurs. Sand sealing also occurs when too fine

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a screen slot is used, which prevents the normal passage of fine-grained materials during development of the well. To repeat, rather than using a too fine slot size distribution, filter pack and development should be optimized for maximum efficiency, while retaining fines. This requires informed engineering, skill, and some significant work time, and thus investment in the well development work. In rock wells, silting may result from an incomplete casing seat, which fails to seal off unconsolidated material. Also, water-bearing fractures themselves may contain fines. These are mobilized by pumping, and may stabilize at a new energy equilibrium after a period of time, or continue pumping fines indefinitely, requiring an engineering response. One poor practice, often employed in developing country economies (and in environmental settings elsewhere—is there a connection?), is the use of filter cloth in well screen to make up for the operational limitations of locally saw-slotted screen. Such filter cloth or geotextile can keep out fines, but fines can also be retained on the cloth (causing sand sealing), or they can bridge with biofouling to rapidly seal off the well, ending the usefulness of a promising water source that brought new hope to a community or of an important monitoring point. Monitoring Wells: Monitoring, dewatering, and recovery wells represent a special case in design and rehabilitation response. Water wells would be completed in favorable sand aquifer zones, and thus avoid many of the problems that wells completed for environmental tasks have with clay, silt, and sand. The mission of such wells, however, is to be completed in discrete horizons to provide samples or contaminant recovery or just a dry trench. For that reason, they are often completed in unfavorable zones, often at the top of the first water-bearing zone or aquifer (broadly defined) encountered. Sometimes screens are designed to straddle the water table. Taken all together, you have the worst possible scenario for well service life. Standard practice in monitoring wells is to complete screened wells with filter packs. These packs usually consist of uniform, rounded quartz sand of an average particle diameter suitable for holding out the more coarse material in a formation. However, selection of pack material and screen involves compromises. The pallet of filter sand that happens to be on the site is one size, not a range of sizes customized for the various wells. The result is that the well screen and pack may not be suitable for retaining the finest material present in a screened interval. Monitored formations are typically highly biologically active (see following), and biological activity can rapidly alter a monitoring well’s performance. Filter Packing Issues: It is also often difficult to properly place the filter pack material in the screen for optimal performance. Well annular spaces are usually small and not smooth. Bridging is highly likely. If the well is more than 40 ft (13 m) or so deep (not very deep), only the tremie methods can ensure that pack material actually reaches the screen. Alternatively, a prepacked screen approach may be considered. Bottom line: Plan adequate annular space for grout and filter pack work. Plan for proper placement. Beyond the inherent technical difficulties are the realities of field conditions. Numerous factors may interfere with exacting well installation. Drillers may be in a hurry because the customer or consultants are pressing to meet a deadline or looking


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at a budget overrun. Supervisors of both drillers and field consultant personnel may want them to press the schedule because they have a backlog to work down. Site conditions may be poor, drilling equipment inadequate for the task (not uncommon), etc. For example, as is typically the case, drilling has commenced in the winter after the planning and approval cycle has been completed (having started after the beginning of the fiscal year). Everyone is cold, it is soggy, and work just does not go as well. The chances for a poor pack are enhanced. The fact that so much good work does get done under the project conditions imposed is a credit to the real professionals of the industry. A typical result, however, from a maintenance standpoint is that many wells have less than optimal screens, packs, and development. Under certain circumstances, especially in pumping wells, well clogging is likely and will have to be controlled so that the wells perform properly. Monitoring wells will produce turbid water that will have to be filtered for analysis, with unknown amounts of contaminants left adsorbed onto the suspended solids, thus affecting sample quality. Unless these are analyzed separately, sample fractions may be lost.

2.3 Yield and Drawdown Problems Lower (or insufficient) yield may result from either hydrogeologic or mechanical causes. Is it the pump or the well, or both (Figures 1.2, 2.1–2.3)? Figure 2.4 illustrates components of the water level system in a well (static water level, pumping water level, and drawdown and its components). Keep this figure in mind as we discuss well performance issues and components throughout the text. Pumping water level decline may be symptoms of zone dewatering or outside influences, such as area or regional water level declines or well interference, or of reduced hydraulic efficiency in the well, resulting from plugging or encrustation of

Figure 2.2 (See color insert following page 66.) Precleaning flow from a clogged well.

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Figure 2.3 Well screen clogged by iron biofouling (North Dakota State University Extension, Scherer, 2005, Circular AE 97).

Static water level

Total drawdown

Aquifer loss

Cone of depression Aquifer pumping water level

Well loss Well pumping water level

Figure 2.4 Pumping well yield and drawdown components.

the borehole, screen, or filter pack. Typical causes of plugging are silt retained in filter packs or biofouling (Section 2.7), and are usually both. Dewatering of an aquifer zone can radically change the local biogeochemistry. Formerly reduced zones become oxidized, changing the nature of chemical constituents and the microbial ecology (Figure 2.5). Such changes affect pumped water quality since constituents may change. Contaminants may increasingly become attenuated. Dewatering or caving in of a major fracture or other water-bearing zone, or loss of connection to water-bearing zones, can be especially dramatic examples of dewatering phenomena.

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Fe III Mn IV & S precip.

Fe III & Mn IV precip.

Fe III precip.

Reduction Ground water flow Increasing Eh

Figure 2.5 Schematic of oxidation and reduction and ecology changes around pumping wells.

Of the mechanical/engineering difficulties, pump problems are much more common. They include pump wear or malfunction, encrustation, plugging (Figure 1.2), or corrosion and perforation of the column pipe, and any increased total dynamic head (TDH) in the water delivery or treatment system. A common situation is the pump that gradually clogs or wears unnoticed, to the point where it can deliver its water discharge rate at just the head in the system. If a nearby well starts pumping, lowering the dynamic water level a foot or meter, the well stops pumping, because the pump simply cannot work against the new head regime. Complete loss of production most typically results from pump mechanical or electrical (mechanical, controls, or supply) failure. However, well mechanical causes may include catastrophic loss of well production due to dewatering, plugging, or collapse. Unless it is a pump mechanical or power failure, usually there is some warning in the form of a noticeable well performance decline. Except for pump mechanical failure, complete well failure usually indicates some lapse or negligence in design, construction, or operation. For example, as reported in Water Well Sustainability in Ontario, a very useful 2006 report produced by the Ontario (Canada) Ministry of Environment, available (at the time of writing) from http://www.wellwise.ca/, a survey of rural well infrastructure by the PFRA in the municipal district of Kneehill, Alberta, concluded that abrupt well failures during times of drought were mostly due to well clogging, not depleted aquifers per se. During these relatively short droughts, the historical range of aquifer water levels was essentially unchanged. Rather, the cause of well failure was felt to be due to the added effect of an increased but unnoticed loss in well efficiency beginning from the time the well was first constructed. In an impaired state, the well cannot function during the low point of the natural range of water level cycles.

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2.4 Chemical Incrustation Figures 2.3 and 2.6 illustrate examples of essentially chemical incrustration. Ground waters typically maintain dissolved solids and gases in solution, even when supersaturated. The types and concentrations of dissolved minerals and gases in the ground water determine whether precipitates will form and how much will be deposited. Slow-moving ground water has ample time to dissolve large amounts of the minerals that it contacts. In most cases, a delicate equilibrium is achieved in native ground water, but pumping a well can upset this equilibrium. Actually, ground water can often be supersaturated with respect to major constituents such as calcite. These changes can result in dissolution from solids and subsequent precipitation and incrustation. In some cases, physicochemical transformations can alter aquifer hydraulic properties, especially when pumping begins (lowering pressure) or changes. Such mineral precipitates can be hard and brittle or can form a soft material like sludge or toothpaste. A commonly found deposit in potable ground water is calcium carbonate (CaCO3). Ground waters contain varying amounts of calcium bicarbonate (Ca(HCO3)2) and carbon dioxide (CO2) in solution. When a well is pumped, drawdown and head loss result. The head or pressure loss near the well bore hole can upset the fine balance that keeps CO2 in solution and it can be released. CO2 is over fifty times as soluble in water as other common air gases, so it does not degas easily. CO2 degassing would be most likely if the pumping water level is significantly deeper than the static water level. Otherwise, it will remain in solution and come on through into the engineered water system unless other mechanisms intervene (Figure 2.7). Still, carbonate clogging of extended hydraulic structures is known from antiquity. A notable example was the circumstances of carbonate clogging in the Roman aqueduct system. The source water for the aqueduct that served the Roman colony at the present city of Nîmes in southern France is high in calcium, low in manganese,

Figure 2.6 Pipe clogged by iron mineral (U.S. Environmental Protection Agency).


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Gas relieved through vent

Gas comes out of solution

Figure 2.7 Schematic of well with gas pressure release.

hard, and alkaline, with most of the hardness being bicarbonate. Extensive deposition due to H+ loss from biocarbonate in a manganese-undersaturated environment resulted in bulky carbonate deposition. Much the same phenomena occur in geotechnical drains (Figure 2.8). As the CO2 comes out of solution, the soluble Ca(HCO3)2 becomes more insoluble CaCO3, which can precipitate within the formation and on the well screen. Magnesium carbonate (MgCO3) can form in a similar manner from magnesium bicarbonate. It is marginally more soluble than CaCO3 in water (which means it is still poorly soluble). Ground water with shifting carbonate species will be revealed by shifts in Ca:Mg ratio compared to surrounding wells in the same aquifer unit. Redox and pH shifts toward oxidation and alkalinity, respectively, may result in the deposition of iron and manganese oxides and carbonates. These shifts, which occur in engineered water treatment aerators, for example, drive oxidation of dissolved iron (Fe) and (under some circumstances) manganese (Mn) to their respective oxidized (and poorly soluble) forms. The resulting oxidized precipitates can form reddish brown or black sludge. Microorganisms accelerate the formation of such deposits, however. In particular, dissolved MnII resists chemical oxidation in ground water of a pH suitable for potable use and requires a microbial mediator for Mn oxides to form (see the following discussion).

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Figure 2.8 Mineral-clogged drain—mostly calcite (Photograph courtesy of Chuck Cooper, Bureau of Reclamation).

Where methane is present and being oxidized to CO2, or CO2 naturally occurs in water due to metabolism or other oxidation of biological material, abundant carbonate deposits may also form when biocarbonates oxidize to poorly soluble carbonates. Oxidation and changes in pH may be aggravated by high near-well turbulence and velocity, oxygen entrainment due to excessive drawdown, and microbial oxidation. Chemical encrustation is also typically a secondary effect of biofouling oxidation or corrosion (Section 2.5 and Section 2.7). Encrustation causes reduced specific capacity and well efficiency and interference with product water quality. Chemical incrustation cannot be eliminated because it is a property of the existing water quality. Geochemistry can, however, be modeled if there is sufficient information, and changes such as precipitation can be predicted (as long as the role of biology—see following—is understood). If proper water quality analyses have been performed prior to construction, the screen can be designed with somewhat larger openings to allow for incrustation or the well system design and operating plan can be modified to slow the changes in equilibrium. Also, a screen material resistant to corrosion, such as high-quality stainless steel, can be selected to allow rehabilitation to remove the incrustation. Plans can also be implemented for periodic treatments to maintain the well’s efficiency.

2.5 Corrosion Pump and well structural corrosion is a very complex phenomenon (Figure 2.9). Corrosion as a term is generally associated with metals, and involves the removal of metal ions from metallic solids in contact with aqueous solutions. As with well and screen design, corrosion is adequately described in the print literature and online. So we summarize here. Causes of abiotic corrosion include naturally aggressive water quality, including waters containing sulfides (H2S or S2–) and chlorides (Cl–), and electrolysis due to stray electrical currents. However, most corrosion has a biological component as well.


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Figure 2.9 (See color insert following page 66.) Corroded submersible pump end (southern Colorado).

Any corrosive situation is aggravated by inappropriate material selection in the design of pump or column pipe, casing, and screen components. Corrosion has secondary effects, such as sand pumping, alteration in water quality (especially elevated metals), secondary system clogging with corrosion products, and structural collapse. Metal corrosion in both fresh and saline water is always the result of an electrochemical reaction. Pure water is a weak electrolyte and is a fair insulator or very poor conductor of electricity. However, it is “hungry” for ions and can be severely corrosive. Sea water and other high total dissolved solids (TDS) waters are strong electrolytes. As an electrical current starts, iron begins to corrode:

Feo = Fe2+ + 2e –

Positively charged ions (Na+, Ca2+, etc.) flow to the cathode (the more noble metallic surface) while the negative ions (Cl–, SO4 –, etc.) flow to the anode. One commonly described manifestation of electrochemical corrosion is the galvanic cell system. A galvanic cell results when two metal surfaces with dissimilar electromotive properties are in contact in an electrolyte. These may be two pieces of metal or places on the same piece of metal that have differing electrical potentials. While useful for conceptual explanation, the galvanic cell is responsible for only a small fraction of corrosion that occurs in potable waters. The principal cause of corrosion in such fresh water is the oxygen concentration cell (or concentration cell corrosion) (Figure 2.10). Carbon steel and stainless steel both develop a coating of corrosion once exposed to oxygen in the presence of water. The chromium in the stainless steel produces a significantly stable coating that electrochemically passifies the surface and inhibits further corrosion. The coating is less effective and stable on carbon steel. The oxygen concentration cell may be initiated by anything that will shield a small area from the dissolved oxygen in the water, such as a grain of sand or a biofilm patch (see Section 2.7.1).

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Sustainable Wells: Maintenance, Problem Prevention, and Rehabilitation 2Fe++ + ½ O2 + 4OH–

2H2O +

4e–

Fe2O3 + H2O

e–

2Fe++ + 4e–

2Fe

4OH– e–

e–

e–

e–

e–

(mild steel)

Figure 2.10 Diagram of a corrosion tubercle in steel pipe.

Concentration cell corrosion can begin at any breach, and often occurs at pipe joints, under gaskets at flanges, threads, and other points of metal stress. Once the coating is breached, either physically by abrasion or by being destabilized (e.g., by Cl–), the point becomes an anode of an electrolytic cell. The surrounding area, which still retains its passifying coating, becomes the cathode of an electrolytic cell. The dissolved oxygen (DO) in the water is in the molecular form as O2. Where the O2 is in contact with the pipe the potential is there to strip electrons from the Fe, even if the surface is uniformly coated with metal oxide. Thus, an electron potential is established between the areas in contact with O2 and where it is excluded. The potential of the cell is dependent on the concentration of dissolved oxygen in the water. The gross potential that is produced may be very small, but the cathode area is large relative to the anode point, which results in a high charge density at the anode. The charge density alone is what provides the energy to the system to strip electrons from the iron and oxidize it to the Fe2+ (ferrous) state:

Feo = Fe2+ + 2e –

The electron stripped from the iron moves through the pipe as an electric current. Fe2+ is soluble under the eH-pH conditions of most ground waters and therefore diffuses away from the anode site. Once started, the cell becomes self-perpetuating and a pit forms. The ferrous (Fe2+) ions produced encounter oxygenated water and are oxidized to ferric (FeIII) hydroxide:

4Fe2+ + O2 + 10H2O = 4Fe(OH)3 + 8H+

The incipient pit becomes covered or surrounded with a crust of insoluble metal oxide or biofilm (Section 2.7), preventing or limiting diffusion of oxygen to the anode. The structure formed is a corrosion tubercle. By ensuring that there will be no oxygen under the tubercle, the electron potential is maintained and the exposed metal cannot reoxidize and repassify, thus perpetuating the process. As indicated above, the further oxidation of ferrous iron to ferric iron liberates hydrogen ions, H+. These migrate to the cathodic areas and form a hydrogen film. Figure 2.11 illustrates some tubercle formations. See also the biological corrosion discussion (Section 2.7.3).

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Outer layer

Shell-like layers Porous interior

1 mm 1 mm

Figure 2.11 Cross section of steel pipe corrosion tubercles (Lytle, Gerken, and Maynard, 2004, U.S. EPA).

Note: In referring to mineral charge states, we will use a superscript numeral (e.g., Fe2+) for an ionic state, as in solution, and Roman numerals (FeIII) in a mineral form. For some minerals (e.g., As for arsenic and U for uranium, we will use parentheses also—As(IV)). Except as it may affect calculation of the Langelier index, pH has little effect on corrosion over the ranges normally found in well waters. However, when the pH of water is below 7, the rate of formation of Fe3+ from Fe2+ and O2 is very much slower than at higher pH values (except when iron-precipitating microflora are involved). Values of pH less than 7 are usually encountered in waters of low alkalinity and low TDS (e.g., water in granite aquifers or representing fresh recharge). Under these conditions, uniform corrosion is more likely to occur (unless iron biofouling is active). Corrosion may be severe in terms of total loss of metal, but in the absence of pitting, perforation will not be rapid and facilities often have reasonably long life. It is the pitting type corrosion that is most often implicated in premature decline in water quality and equipment failure. Perforation of casing by pitting corrosion that results in a coliform-bacteria positive test result can doom the entire well. Corrosion of steel under nonpitting circumstances is inhibited by the formation of calcite layers on metal surfaces. CaCO3 saturation is governed by pH, temperature, and the water’s ionic strength. The values of solubility constants depend upon the temperature and the degree of mineralization (ionic strength) of the water. Simplifying: At 25°C and moderate mineralization (400+ mg/L total dissolved solids) the situation can be described by

pHs = 11.85 – log [Ca] – log [HCO3]

(2.1)

In wells, the portions of the casing and column above the water level are usually covered with condensate saturated with air. Since air contains CO2, the condensate water may contain carbonic acid and locally have a pH of less than 7, and TDS will be very low. Nonpitting sheet corrosion may be expected to occur.

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One problem with extrapolating from empirical observation to concept is that water quality data reported from corrosion incidents are seldom complete. Hardness may be reported, but not alkalinity, or hardness (as what?) is tested, but no bicarbonate data collected. DO and other dissolved gases such as CO2 are seldom reported, and they are major drivers for corrosivity. Note: Corrosion potentials and symptoms are different in sea water (for which much of the corrosion literature is written) and fresh water. Specifically of interest for wells is that corrosion between dissimilar metals is confined to a few millimeters in distance, and is more likely to occur at welds, fastenings, threads, or other alterations.

2.6 Plastic Deterioration Plastics are routinely used in well and pumping equipment due to their resistance to corrosion, smoothness, light weight, and flexibility. Polyvinyl chloride (PVC), fluoro carbon (e.g., Teflon), and polystyrene formulations used in casing and pump com ponents are indeed recalcitrant, that is, not susceptible to corrosion, by themselves. PVC becomes subject to deterioration if it contains a significant percentage of plasticizers; however, PVC specified for water use (designated NSF-pw) forms a rigid product that contains a low level of mobile plasticizers. Hydrocarbons are known to penetrate PVC pipe, however, and may serve as a means of softening PVC bonds and making its polymer components available for biodegradation in some circumstances. Where solvent welding of casing sections is practiced, transient detections of solvent components occur, usually only early in the well’s life. Casing plastic cement bonds are softened and broken when certain organic compounds are present in ground water.

2.7 Biofouling—A Hitchhiker’s Guide to How Life Takes Over Who Are Those Guys?: In the movie Butch Cassidy and the Sundance Kid, the main characters (likable criminals) are tracked after a botched robbery for a long time by determined and skillful trackers. They repeatedly ask, “Who are those guys?” as they desperately try one trick after another to shake the posse. Wells and associated systems are usually designed by well drillers, sometimes engineers, and (if the planner is prudent) geologists. Naturally, plugging by sediment (sand, silt, clay) has traditionally been the most often recognized cause of well plugging and reduced performance. Water sample quality is affected by what are described as colloids. However, experience with a wide range of well types (water supply, dewatering, recovery, recharge, and monitoring) around the world suggests that the number one contributor to reduced well performance in most regions across the globe is biofouling, which can be defined as the impairment or degradation of something (well, ship’s hull, catheter) as a result of the growth or activity of living organisms. It occurs in a broad range of systems.


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Who are those guys? As in the movie, knowing what you are dealing with is important when trying to develop a solution. The key words here are experienced, adaptable, and survivors. In the case of microbial actions, good evidence indicates that cellular microbial life was present over 3.4 billion years ago. By that time, microbes were forming biofilms and complex structures (stromatolites) and interacting with their environments under more lethal conditions than exist today (higher UV influx, for example). They survived young Earth conditions that very nearly wiped out life more than once. Over the intervening thousands of millions of years, microbes have reached the deep terrestrial subsurface and the deepest ocean. They use a wide range of processes for respiration. Their genetic systems allow for borrowing genes from the environment. They can survive brutal conditions on present-day Earth. Other organisms, especially fungi and plants, have thrown up ingenious and complex antibiotic defenses against bacteria. The microbes have seen it all. Keep that in mind as you consider preventive and treatment measures. Other Causes Contribute, but … Where silting is indicated as a cause of well plugging, it is most likely working in tandem with biofouling plugging at or near the intake surface and the portion of the aquifer matrix subject to partial oxidation. Likewise, many alterations of chemistry and formations of physical properties can occur due to biological action depending on the circumstances: carbonate deposition, gas formation, oxidation, and reduction. So who are these guys? Biofouling involves the biological formation and deposition of fouling materials, which usually include mineral and metal precipitates (e.g., Fe oxides and sulfides, Mn, S oxides, and CaCO3). Because of its importance, biofouling and its adjunct—biocorrosion—will be discussed here at length. We also specifically refer you to Microbiology of Well Biofouling and Practical Manual of Groundwater Microbiology by D. R. Cullimore (see our recommended reading list) to get a more in-depth and poetic assessment of the subject of biofouling.

2.7.1 Biofilm and Biofouling Basics Biofouling and other biomass-driven effects of living things can take many forms in engineered systems, from zebra mussel clogging of surface water intakes or irrigation gates to fairly benign coatings in all sorts of industrial systems, both on the surface and underground, and everywhere in between. Biofouling is also a medically important phenomenon: coating catheters, aiding antiobiotic resistance, and more. Figure 2.12 illustrates a typical mixed biofilm. Biofouling begins with the development of biofilms. These biofilms are complex biological coatings. Bacteria that form biofilms are considered to be ubiquitous in terrestrial and aquatic environments. The impulse to form biofilms is also ubiquitous and ancient in nature. Fossil evidence shows that marine microbes formed biofilms at least 3.4 billion years ago. Naturally, biofilm-forming microbes adapt to novel

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Figure 2.12 (See color insert following page 66.) Mixed biofilm from water well samples (normal light photomicrograph).

environments. Biofilms and biofouling also occur on medical appliances, in laboratory systems, and even in our own bodies (complications of cystic fibrosis being the most extreme example in humans), in addition to aquatic or marine environments. Biofilms are typically formed by bacteria (and cyanobacteria), but they typically include diatoms and other algae, protists, and small multicellular animals such as rotifers, where conditions permit. In wells, biofilms are almost entirely bacterial. However, protists (usually ciliates) are common. Figure 2.13 illustrates some macroscopic manifestations of biofilm formation. Figure 2.14 illustrates some really chunky biofouling. Zebra mussel and quagga mussel and similar biofouling that involves macroorganisms can cause severe metal corrosion and iron deposition, as these aggregations attract and support bacterial biofouling by providing abundant organic material and growth surfaces. Mussel verligers (some as small as 2 μm) can find their way down fractures out of reservoirs and Rant Speaking of zebra mussels, here in North America and elsewhere, we pay a constant, undefined tax—dealing with the costly side effects of greed in world trade in the form of exotic species introduced into our ecosystems. The shipping industry says it is too costly to manage ship ballast water with the least bit of responsibility, so our cities and power stations and fisheries are expected to pay for cleaning off their mussels. Sports fisheries people in their careless ignorance have now spread these to the waters of the U.S. West. Our foreign trade partners cannot be bothered to inspect and disinfect pallets. So we get Dutch elm disease and ash borers. We Americans nearly destroyed the European wine industry with vine root parasites. No wonder some people are socialist and protectionist. This is the thanks we get for supporting globalization?


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Biofilms Forming

Seep in tunnel (above L), Fe biofouled pipe (above R) and trickling water treatment (right)

Figure 2.13 Examples of manifestations of biofouling.

Figure 2.14 Zebra mussel fouling in pipe (Gemma Grace, Ontario, Canada).

into pressure relief drains, for example, so they can on occasion become a ground water issue. They are certainly a utility and facility maintenance issue. 2.7.1.1 Biofilms and Microbial Survival Biofilms have a survival function for microorganisms in aquatic and soil environments. One is to provide, on a microscopic scale, multiple environments within the biofilm, allowing for the survival of a variety of microorganisms (collectively referred to as a consortium), transport of nutrients, and physicochemical gradients. Multicellularity is an advantage to the community or consortium. Some members are good protectors, others best at recycling the dead, and so forth. An important factor to remember is the complexity and adaptability of biofilm communities—in economic terms, these are diverse, innovative economies, not “company towns.” Biofilms also serve to protect living cells within them from external stress, such as disinfectants or designer biocides. Fe-, S-, and Mn-precipitating bacteria in these

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biofilms precipitate metallic oxides and extracellular polymers (ECPs). Anaerobic bacteria associated with biofilms produce reducing agents (e.g., sulfides and methane). All of these can react with and effectively neutralize oxidants such as chlorine, oxygen, and hydrogen peroxide. Buffers generated by the bacteria and their biofilm matrices likewise can dampen the effects of acids or caustics used in well treatments. Plus, the biofilm matrix itself can take a “burn” while cells inside retract and adapt to the toxic conditions. Together, what you have is an example of a complex adaptive system (CAS): a system that is complex (having multiple resources—in this case, multiple, flexible genomes and enzymatic systems) and can adapt (brings these resources to bear to meet challenges). Societies, economies, and ecosystems are other examples of CAS. 2.7.1.2 Biofilm Function and Ecological Function Many of you with ecological or agricultural experience understand the value of plants in anchoring unstable slopes. Recent University of Colorado research in Peru has documented the role of microorganisms in stabilizing talus and unstable soil in extreme conditions immediately after glacier retreat at high altitude. At their research site at the Puca Glacier, microbes stabilized the soil and prevented erosion on the slope by using their filament-like structure to weave soil particles together in a matrix. The CU-Boulder researchers also found the microbes excrete a glue-like sugar compound to further bond soil particles. Does that sound a little like what happens in a pumping well over time (see following)? In addition, the University of Colorado researchers discovered that nitrogen fixation rates—the process in which nitrogen gas is converted by the bacteria into compounds in the soil like ammonia and nitrate—increased by about a hundred-fold in the first five years after exposure of the soil. It should not be overlooked that microorganisms in the environment (working in consortia as complex adaptive systems) have adaptive functions or behaviors that can find expression in our engineered systems. 2.7.1.3 Biofilms and Biofouling in Ground Water It should hardly be surprising that aquifers often contain large, active, microbial populations. Aquifers are (1) formed from sediments or (2) fractured rocks (also sedimentary in most cases) with interconnected fractures. Fracture or pore apertures greater than 1–2 μm permit migration of microbial particles (Figure 2.15). In ground-water source systems, microbial biofilms are the predominant habitat for aquifer microflora (Figure 2.16). From a microbial standpoint, aquifers are ideal environments in many cases, especially if suitable organic substrates are present. There is tremendous surface area for colonization, moderate temperatures, nutrient flux, and overall very little disturbance. Because the surface areas of the interstitial spaces in an aquifer are very large, the total mass of biofilms around a well can be likewise large given the right conditions. As these biofilms accumulate cell material and debris over time, they accumulate biomass. Such biomass is the basis for biologically mediated encrustation in water wells and is implicated in associated corrosion. Where significant amounts of hydrocarbons and other assimilable organic compounds (AOCs) are mixed with water, large populations of the many microorganisms

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Re-entrainment: Size preference unknown

Earth matrix Dispersion

Sorptive filtration: Preferential attachment of smaller bacteria

Pore spaces vs. microbe size – conditions affect bacteria size, types, attachment

Advection

USGS

Figure 2.15 Bacterial size, movement, and attachment in relation to pore size in aquifer materials (U.S. Geological Survey).

Figure 2.16 Iron-related biofilm from well water samples (normal light photomicrographs).

that can utilize these compounds also occur. This is particularly the case where in situ bioremediation is encouraged by the addition of microbial nutrients, cometabolites, and electron acceptors (PO4, NO3, O2, etc.). A widely observed phenomenon in ecology is that community diversity and total live biomass are greatest where there are gradients, such as forest edges. In the microbial realm, these gradients are primarily physicochemical in nature, and can occur over microscopic to centimeter distances.

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A variety of environmental gradients can be expected to be formed by biogeochemical processes in aquifers. Such processes are enhanced in aquifers with notable AOC concentrations. AOC concentrations may be sufficient to encourage microbial growth and sharp changes in redox potential. Add pumping wells and you have especially rich environmental diversity. These gradients facilitate (and are the product of) a variety of microbial activities. This variety is reflected in a high overall microbial diversity in relatively rich ground water, although single species may dominate locally or transiently in time. Fermentation, chemoheterotrophic oxidation of organics, and both oxidation and reduction of minerals and metals are practiced by microorganisms all living in close proximity. Case History Example: Organics Contamination of Iowa Wellfield—Species Diversity Apparently as a result of leaking organics-laden carbon dioxide from a pipeline, a large wellfield was affected by an intense increase in bioavailable organic material in the aquifer. In a study that sampled formation material and analyzed microbial diversity, the biodiversity of aquifer sediment cores was greatest right at the alledged point of release, decreasing away from the release point.

More hydrophobic organics (e.g., hydrocarbons) may adhere to particles where the biofilms form, so that the bacteria present have an especially favorable situation for mass growth. Hydrocarbon-water interfaces provide a favorable growth situation as well. On a soil particle coated with dilute product, both situations occur (solid and oilwater interfaces), providing more variety in growth conditions (Figure 2.17). Clogging deposits coating particles rapidly fill pore spaces, throttling hydraulic conductivity. The microbial ecology of a near-well system of a ground-water remediation system (such as one that incorporates pumping and venting) may be quite complex (Figure 2.18), with molds and other microbes that form elaborate three-dimensional Product

Interface biofilm

Mixing zone Organic coating and biofilm Water

Figure 2.17 Soil-water-oil-biofilm interface.

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Causes and Effects of Well Deterioration Mold spores aerosol-borne bacteria

Well

Soil ventilation

Biodegradation & organic acid formation

Molds

Smeared product

Vapors

Molds

Product

FeIII, MnIV, S0/SO4 reduction Fe, Mn, S biofouling

Redox fringe Fe, Mn, S biofouling, clogging and corrosion

Figure 2.18 Microbial ecology schematic of a remediation system.

structures occupying the unsaturated zone above the water table, anaerobic dissimilatory metal reducers occupying the anaerobic ground water, and metal oxidizers and hydrocarbon utilizers found mostly at the interface between the aerobic and anaerobic zones. One can expect that microorganisms will function in such constructed environments as if the system were a disturbed environment, expressing filamentous and adhesive and other system-modifying functions, such as nitrogen fixation and nutrient hoarding.

2.7.2 Water Quality Degradation: Monitoring and Remediation Problems Typically, the earliest noticeable manifestation of biofouling in any well is the water quality change that accompanies mass bacterial growth and associated Fe, Mn, and S transformations. Fe and Mn occurrence and concentrations in ground water are affected by several complex mechanisms with microbial and physical-chemical components, including feedback controls over rates of activity. Turbidity increases, filters are clogged, or filtration of samples becomes necessary. Odors may change or form. Supersaturation of CO2 and CH4 and subsequent off-gassing can occur. This can be alarming, or at the very least troublesome operationally (and occasionally lethal to animals). These are further symptoms of microbial processes, either in the wells involved or in the source water. Biological interaction with transient pulses of organics reflects passages of spill components. Figure 2.19 depicts a hypothetical relationship of this type.

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35

Organic Chemical and Bacterial Data, Affected Water Well 2 million cells/mL

30

ug/L

25 500,000 cells/mL

20 15 10

1000 cells/mL

0

May-89 Jun-89 Sep-89 Nov-89 Jan-90 Mar-90 May-90 Jul-90 Sep-90 Nov-90 Jan-91 Mar-91 May-91 Jul-91 Sep-91 Nov-91 Jan-92 Mar-92 May-92 Jul-92 Sep-92 Nov-92 Jan-93 Mar-93 May-93 Jul-93 Sep-93 Nov-93 Jan-94 Mar-94 May-94 Jul-94 Sep-94 Nov-94 Jan-95 Mar-95 May-95 Jul-95 Sep-95 Nov-95

5

Dates

TCE ug/L

Vinyl chloride ug/L

Vinyl chloride MCL ug/L

ds-1, 2-dichloroethene ug/L

TCE MCL ug/L

Figure 2.19 Passage of a contaminant plume in an alluvial aquifer. This is a simulation based on observed phenomena. Usually indications of microbial activity are detected months or years later in response to some observed problem.

Discoloration, high bacterial counts, high turbidity (excluding sediment), and odor are symptomatic of active, established biofilms present in and around the pumping well. Portions of biofilms will intermittently slough off into the water being pumped through the collection-distribution system to the treatment plant or distribution system. Transient, elevated Fe, Mn, and H2S concentrations in pumped ground water, and increases in levels at the leading edge of a contaminant plume, are typically the result of stimulated bacterial activities in the aquifer. The bacteria metabolically reduce FeIII, MnIV, and SO42–, thus mobilizing soluble Fe, Mn, and S species. Subsequent sloughing of FeIII and MnIV biofilms containing sulfide products adds to total metal contents. Figures 2.5, 2.20, and 2.21 are summary representations of Fe, Mn, and S transformations in aquifers, especially around wells. Metallic oxides (predominantly Fe hydroxides) produced by corrosion and FeIII precipitation due to biofouling are important reactive surfaces. They interact with charged species such as H+ (thus affecting pH), Cd2+ and other metallic cations, and anions such as SO42, as well as organic compounds. MnIV and FeIII oxides can thus scavenge heavy metals such as Co, Ni, Cu, Zn, and Sn, for example. Fe sulfides and hydroxides are also involved in the immobilization of soluble U(VI). With changes in drinking water arsenic (As) regulations, control of As has become an important ground-water quality issue. Soluble As is readily scavenged and held by FeIII oxihydroxide surfaces. Where soluble Mn is present in ground water, it is also complexed with the FeIII oxides. Where ground-water redox potential is reducing, low-solubility As(V) can be reduced to mobile As(III). In heavily biofouled wells, this transformation can occur in the reducing conditions of sediment-filled sumps, or where low-Eh ground water encounters As-containing sediment.

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Free Fe2+, Mn2+, S2–

FeIII, S, MnIV oxides on matrix Sulfide/sulfate & carbonate minerals

Methane and CO2

Biofilm oxidation retention

Sulfide/sulfate/carbonate minerals interspersed

FeIII, S, MnIV oxides carbonate Biofilm

Microbial reduction & mobilization

Figure 2.20 Fe, Mn, and S transformations and mobility in aquifers—a schematic of typical occurrences in a biologically active mixed reducing-oxidizing aquifer system.

Sh m ed s et lu al gs se o tc f .

Pipe surface

Detail

Typical: FeIII oxide outside, FeII sulfides inside

Uptake heavy metals etc. Biofilm

Perforation from MIC

Plugging at oxic-anoxic interface

Plugging at oxic-anoxic interface

Clogging intake & impellers sulfides & oxides

Screen and filter pack FeIII oxides, carbonates, FeII sulfides (clogging)

Figure 2.21 Fe transformation and plugging zone around an affected well—a schematic of the many activities and results of activity in the busy environment of a pumping well.

Many types of microorganisms can selectively precipitate minerals. Microbial reduction results in forming insoluble U(IV) from soluble U(VI), potentially immobilizing uranium in the subsurface. In a similar case, a variety of bacterial and archaean species have been identified as facilitating the capture and reduction of gold chloride to elemental gold in soils. Both can result in minable ore deposits.

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Levels of organic constituents detected in monitoring well samples may become erratic over time. This may be the result of partial attenuation on soil particles, followed by release in sloughing events, but biofilms also may cause partial attenuation and sloughing. FeIII hydroxide minerals associated with biofilms are highly reactive with reduced organic compounds. The cycle of adsorption, partial utilization, and slug release results in sample interference and data that indicate irregular concentrations, or show breakdown products and “unknowns” in organic analyses. Microbially mediated FeIII and MnIV reduction and FeII and MnII mobilization result in dissolved Fe2+ and Mn2+ in ground water, with pronounced differences along flow paths from recharge to discharge areas. Crystalline FeIII is reduced by bacteria in aquifer materials, with the rate of reduction and dissolution controlled by FeII in solution. Mn and Fe complexed with ECP may occur in suspension, and can be detected in high levels in analytical results from unfiltered samples. This is a process that is analogous to Fe sequestration treatments used to control Fe and Mn precipitation in water distribution systems. Conversely, biofilms may also act as metal filters, removing Fe and possibly Mn from solution. Once the well biofilm has been removed or inactivated during rehabilitation treatment, Fe and Mn levels may increase in the produced water due to the lack of a sequestering effect previously provided by the biofilm. The result is that biofouled wells (both production and monitoring wells) typically exhibit fluctuating raw water constituent (e.g., Fe and Mn) levels (both soluble or colloidal). And you may think you are collecting representative water samples from the aquifer from your monitoring well; however, such samples may actually be products of microbial and other well-associated redox modifications. If you drive a probe into the aquifer several meters away, you may get out of this bioactive zone and thus encounter unmodified aquifer water (maybe). Intermittently high Fe and Mn levels can have a considerable effect on the operation of water treatment plants. These effects include increased chemical oxidant demand, bleed-through of filters, increased system hydraulic head, and more frequent filter backwash and aeration tower cleaning intervals. These biologically mediated water quality changes can be particularly troubling when FeIII oxide or S-slime deposits clog pipelines (typically not very large in diameter in remediation systems) and coat carbon filters or aeration tower media. It is clear that microbial effects can be very important influences on monitoring and recovery wells, just as they are for water wells, and dealing with these effects needs to be a part of design and operation (Chapters 4 through 6). This discussion of microbial transformations of elements and compounds is brief and intended to provide the reader with an introduction to causes. The reader should realize that after probably 3.5 billion years of cellular life history, the range and complexity of microbial systems and actions is vast. Readers interested in a detailed review of geomicrobiological transformations are referred to Geomicrobiology, fifth edition, by H. L. Ehrlich and Dianne K. Newman (recommended reading list).

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2.7.3 Microbially Mediated Metallic Corrosion Microorganisms accelerate corrosion of well and water treatment system metallic components in a variety of ways. The microbial enhancement of corrosion is related to the production of corrosive metabolites such as nitric and other mineral and organic acids (which act as metal scavenging anions) and sulfides (S2–), as well as the establishment of differential oxidation cells in the form of colonies or biofilms. The formation of these cells creates conditions for anodic dissolution of metals, particularly iron. Likewise, FeIII-reducing bacteria have been demonstrated to reduce Fe oxide coatings on steel, stimulating corrosion. Fe biofouling is typically not uniform, and areas of differing electron potentials result on biofouled surfaces, providing local environments conducive to corrosion. When differential oxidation cells form, electrochemical corrosion occurs at areas (anodes) of lowest oxygen concentration, for example, under a biofilm. In addition to providing a diffusion barrier to oxygen mass transfer, the microorganisms present in biofilms consume available oxygen by aerobic respiration. Figure 2.22 is a schematic of microbial corrosion processes. When oxygen depletion occurs, anaerobes such as sulfate (SO4)-reducing bac teria (SRB) can proliferate if suitable organic carbon sources are present. They seem to be virtually ubiquitous in aquifers, even those with overall high bulk Eh. SRB can utilize molecular hydrogen and produce S2–, both of which are important in electrochemical corrosion. In addition, biofilms shelter other heterotrophic bacteria that produce acidic metabolites that are corrosive or serve to promote or maintain reducing environments that benefit the SRB. One example is the production

Biofilm surface

Biofilm

Hardened tubercle

Organic acids: Metal corrosion

n tio tra ne Pe

Metal surface

Metallic sulfides magnetite

Re

x do

t ien ad r g

Biofilm

Redox gra dients: Electron movemen t

nt

die

ra xg edo

R

Metal oxides

Crevice

Figure 2.22 Microbial corrosion processes schematic—illustrating the range of bioelectrical activity around a corrosion tubercle on a steel surface (some features also apply to crevice corrosion of stainless steel alloys).

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Figure 2.23 (See color insert following page 66.) Example of mild steel well pump discharge pipe tuberculation. Biocorroded stainless steel monitoring well casing

Hole at 10 ft 4 in Start of anode development only (left)

Figure 2.24 Microbially influenced corrosion of Type 316 stainless steel monitoring well casing. Section at left has begun anodic attack under biofilm associated with bentonite grout, while in the section on the right, corrosion is associated with metal fatigue.

of short-chain organic acids during incomplete anaerobic oxidation of long-chain aliphatic hydrocarbons. Microbially induced corrosion (MIC) of ground-water well components is widely recognized and associated with degradation of mild steel (Figure 2.23) and even Type 304 stainless steel, but sometimes also more resistant classes of stainless (Figure 2.24). Corrosion of stainless steel components of monitoring wells has been implicated in the alteration of sample water quality. Such metal corrosion processes are accelerated in recovery well systems controlling organic plumes, due to both the presence of organics that are degraded to organic acids, and the overall intensity of microbial activity. This microflora may additionally include a wide range of fungal growth and functions where wells and


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sediments are frequently unsaturated. Thus, there is a complex overall biochemical situation that encourages multiple electron potential cells and corrosion. A common expression of metallic corrosion in monitoring and pumping wells is intergranular corrosion cracking. Corrosion initiates in heat-affected zones such as weld areas of wire-wound screens at features called nodes, and spreads. Nodes may have small external openings, but large subsurface expression. Heated austenitic steel is sensitized at 950–1,450°C, with chromium depletion at intergranular boundaries. Biofilms interfere with the oxidation at the metallic surface necessary for repassivation of the stainless steel by forming differential oxidation cells. Biofouling proceeds as in mild steel.

2.7.4 Iron, Manganese, and Sulfur Biofouling Fe, Mn, and S biofouling can be considered together as a particular case in the biofouling topic, primarily because of its prevalence and impact on the performance of well systems and downstream piping and treatment. Such biofouling is complex, and is a factor in the water quality and corrosion effects just discussed. 2.7.4.1 Fe, Mn, and S Biofouling: What’s Happening Microbiological activities are now regarded as the most important factor in the oxidation-reduction reactions that take place in ground water for both inorganics and many organics, even under anaerobic conditions. Bacteria are able to utilize substrates such as hydrocarbons as carbon sources in the absence of oxygen by using other electron acceptors, such as Fe3+, SO4, and NO3, in respiration. Microbially mediated redox reactions can be complex and add greatly to the problem of fully understanding the geochemical environment in an aquifer setting (Figures 2.5, 2.20, and 2.21). Shallow aquifers rarely have such low redox potentials that organic-oxidation reactions are not favorable, unless the organic content and microbial activity are quite high and oxygen entirely depleted. This, of course, is likely to be the case when hydrocarbon contamination occurs. In ground-water-source (GWS) systems, biofouling usually involves the oxidation of Fe, Mn, and S compounds by bacteria. These compounds become part of biofilm complexes, including the Fe, Mn, and S compounds, ECP, and the bacterial cells themselves. Fe and Mn biofouling can vary from being a minor nuisance to a cause of major maintenance problems, even resulting in complete abandonment of wells and wellfields. Fe- and Mn-biofouling problems are well documented, with numerous reports published in a variety of water supply and ground-water industry literature based on experience from North America and around the world. S-slime biofouling is much less well documented, but typical of wells operating in sulfide-containing ground waters (including those recovering hydrocarbons), where oxidizing conditions exist in pumping wells. Problems include clogging of pumps, drop (discharge) pipes, screens, and filters by slimes (Figures 1.2, 2.3, and 2.13) and subsequent precipitates, such as Ca sulfate, and associated corrosion of metal pump components.

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Microbially mediated Fe, Mn, and S transformations also play an integral role in fouling attached water collection and treatment systems. As in wells, corrosion and the formation of encrustation and slimes, and changes in Fe, Mn, and S content and form in pumped water, occur downstream. 2.7.4.2 How Fe, Mn, and S Biofouling Occurs Fe and Mn biofouling may take many forms and may be caused by both direct and indirect or passive microbial processes. FeII compounds (ferrous Fe) or ions (Fe2+) can also be oxidized to the FeIII (ferric) state by nonbiological (abiotic) oxidants such as chlorine or oxygen. However, kinetic estimates for conditions relevant to ground-water conditions indicate that abiotic rates of Fe oxidation are not sufficient to account for the relatively rapid clogging problems experienced in ground-water extraction systems. Autooxidation of MnII to MnIV rarely occurs abiotically under ambient conditions, requiring a redox potential of 600–800 mV at pH 7. In aquifers with typical >0.1 mg/L total organic carbon levels and bulk Eh-pH conditions in the stability range for dissolved species of Fe and Mn, abiotic processes are unlikely to be the immediate cause of FeIII and MnIV oxide precipitation. Some bacterial strains associated with iron biofouling have been demonstrated experimentally to actively (enzymatically) oxidize Fe and Mn for various purposes, and others are suspected, especially the common neutrophilic (prefers neutral pH) iron bacterium, Gallionella ferruginea (Figure 2.25). Besides direct enzymatic

Figure 2.25 (See color insert following page 66.) Gallionella-dominated water well biofilm (normal light photomicrograph).


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Figure 2.26 (See color insert following page 66.) Mixed filamentous biofilm featuring MnIV oxide mineralogy (normal light photomicrograph (PMG)).

oxidation, FeIII and sometimes MnIV oxidation is also favorably mediated by microbial structures and reaction with ECP under common ground-water conditions (Figures 2.26 and 2.27). Iron oxidation can also be driven anaerobically by reduction of nitrate. CO2 generated by microbial respiration drives carbonate equilibrium toward bicarbonate saturation, and microbial cells cause precipitation of various carbonate minerals near or on their cell surfaces. These and other microbial effects (descriptions of which occupy entire chapters in Geomicrobiology) tend to complicate geochemical estimating. Microbial oxidation of sulfides results in the familiar white slime phenomenon of wells and sulfur springs. Sulfur-oxidizing bacteria (SOB) have been found to be relatively common in aquifer sediments and also in wells developed in S2–-containing ground waters (Figure 2.28) and in relief drains in dams (Figure 2.29). S0 has a narrow stability range (Eh approximately 200–400 mV vs. pH 4–2) under the very specific environmental conditions of Eh-pH stability diagrams published by the U.S. Geological Survey (see recommended reading). Bacteria precipitating S0 apparently provide this environmental condition in their biofilms for as yet unknown reasons. The expression of S biofouling resembles Fe and Mn biofouling in that soluble S2– is oxidized and precipitated as S0 in biofilms at some point where the O2 reaches some (as yet unknown) threshold. S-biofouling (white slime) occurs when Fe2– is typically absent or present in very low levels or otherwise the S2– is taken up as FeS minerals.

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Rehydrated biogenic MnIV oxide particle

Emerging bacterial cells in biofilm matrix

Emerging filament

Figure 2.27 Filamentous Mn-precipitating bacteria reemerging when MnIV oxide particles (black) are rehydrated (Bureau of Reclamation–Stuart Smith PMG, annotated by SAS)— minutes after adding water.

Figure 2.28 Sulfur oxidizing biofouling in well pump discharge pipe, South Africa (Courtesy of Hose Solutions Inc.).

2.7.4.3 The Redox Fringe Redox zonation is a feature of aquifers, both those in close contact with the surface and those without such oxygen influence. Boundaries may be abrupt, especially in aquifers containing high levels of reduced ions and organic compounds. The boundary zone between zones containing and depleted of free dissolved oxygen appears to be an important environment for the mass occurrence of


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Figure 2.29 (See color insert following page 66.) Thothrix-dominated sulfur-oxidizing biofouling of geotechnical drains (Bureau of Reclamation–Stuart Smith photographs).

FeIII-precipitating biofouling organisms. D. R. Cullimore coined the term redox fringe (redox front is also used) to describe this oxygen depletion boundary in ground water, where dissolved FeII species are oxidized to FeIII (see Figures 2.5, 2.20, and 2.21). The precise Eh values in which Fe, Mn, and S transformations occur, of course, also depend upon pH and other physical parameters. Valid Eh determinations are notoriously difficult to make in natural and contaminated ground water due to the variety of redox-active compounds present, as well as complicating microbial influences such as providing catalytic surfaces. Hydrolysis of FeIII leads to formation of complexes of FeIII oxides with bacterial ECP. MnIV oxide formation, complexation, and precipitation occurs in much the same way. Microbially facilitated FeII, MnII, and S2– oxidation occurs, followed by deposition of FeIII and Mn(III and IV) oxides and elemental S.

2.7.5 Effects on Performance of Well Systems: A Summary The extent and effect of Fe, Mn, and S oxidation and precipitation and associated biofouling in any particular situation depends on a variety of environmental, hydraulic, and use factors in the well or the downstream receiver of its production, such as a treatment system. These effects may be dramatic or hardly noticeable in the short term. Probably the most adverse effect of Fe and (theoretically) Mn oxidation and biofouling is systemic plugging of near-well-aquifer pore volume through an entire aquifer unit.

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Previous studies of core samples obtained adjacent to clogging wells have shown significant biofilm presence and plugging around wells. Filling of the interstitial space and resulting permeability reduction by 65–99% may locally occur. However, in the limited studies available, Fe and Mn biofouling, like S biofouling, is rare in aquifer samples away from the near vicinity of wells unless oxidation is deliberately induced (e.g., with in situ aeration installations designed to remove Fe and Mn in situ or aeration for in situ bioremediation). However, widespread porosity clogging by FeIII oxides is certainly possible based on the example of massive, low-permeability FeIII oxide ores deposited in sandstones and formerly unconsolidated deposits that typically serve as aquifers, known locally as bog ores. Such ore deposition is considered to have a microbiological origin. Europeans have used such deposits since ancient times (including Norse settlers and explorers in Iceland and coastal North America). Americans have “iron bacteria” to thank for these locally important ore deposits that were used for making cannons and other ordinance during our wars of independence from the British empire. Processes occurring in unconsolidated aquifers treated with in situ aeration to remove Fe and Mn are likely also to occur in aquifers aerated for in situ bioremediation, and probably in any drawdown cone around a well. Likewise, the Eh-pH and filtration conditions of a biological iron filter plant are favorably recreated in the redox fringe around filter packed wells and subsequently in downstream treatment systems. Of course, this is happening without the efficient backwash systems designed in engineered filters to keep the filter media clear. Do you want some free engineering advice from the ground-water science people? Do not treat your water for Fe and Mn in the aquifer. Treat it aboveground in an engineered water treatment plant, where it belongs. Or at least trickle it down a slope instead. The more typical case is that aquifers with waters that exhibit relatively low Eh levels overall contain an indigenous microbial community capable of reducing FeIII, SO4 and possibly MnIV. The Fe-, Mn-, and S-oxidizing and -precipitating biofouling itself, associated with aerobic metabolism, occurs at the oxidation-reduction interface (redox fringe). The redox fringe (Figures 2.5, 2.20, and 2.21) occurs near the water table, wells and springs, and along organic contaminant plume fronts, as described. In well systems, S slimes that impede flow seem to occur (1) when there is both significant dissolved S2– and O2 available in the pumped ground water and (2) in boreholes or downstream at meters, particulate filters, or other restrictions. Such well systems provide conditions similar to those at spring outfalls where sulfur slimes are found naturally. Figure 2.30 is a white sulfur spring, but not actually natural. In the well itself, biofouling phenomena may encrust or loosely plug well borehole intake areas and screens, pumps, and other equipment (Figures 1.2, 2.3, and 2.21). The initial process is the formation of a biofilm on surfaces in the well (casing, screen, etc.) and the aquifer matrix in the vicinity of the well. Figure 2.31 illustrates the process of biofilm attachment and development on a surface (whatever the surface may be). View 1 illustrates initial adherence and attachment. View 2 represents the maturation of the biofilm structure, including the formation of complex threedimensional structures. View 3 represents some of the ways that biofilms spread.


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Figure 2.30 (See color insert following page 66.) White sulfur biomass associated with artesian spring (in actuality, an uncontrolled well) in western Ohio.

Figure 2.31 Schematic presentation of the initiation and development of a biofilm (P. Dirckx, Montana State University Center for Biofilm Engineering).

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In a relatively oxygenated well environment, typical of pumping wells, Fe-, Mn-, and S-depositing biofilms may form within weeks and biofouling within weeks or months. The time course of this process, resulting in water quality or pumping problems, may vary considerably. 2.7.5.1 Hydraulic Impacts Hydrogeologic conditions affect the impact of Fe, Mn, and S biofouling on the well. For example, wells in highly transmissive gravels or rock aquifers do not tend to plug at the borehole wall even if they may be experiencing significant biofouling. Fractures and solution channels intercepted in these formations typically have such a large volume (and volume-to-surface ratio) that hydraulically noticeable plugging is improbable in most cases. On the other hand, poorly or moderately transmissive porous-media aquifers and filter packs have lower volume-to-surface ratios and are more vulnerable to plugging. Zones in which FeIII oxyhydroxides are precipitated may be quite narrow, resulting in bands of Fe oxides forming locally around wells. These form microartesian conditions (tiny confined zones) in our experience. Biofouling effects on pumps and discharge pipes, as well as downstream water collection and treatment system components, can be dramatic. Fe, Mn, S, and combination deposits break loose and enter the pump, leading to clogging problems (Figures 1.2 and 2.3). Biofilms on interior pipe walls become increasingly hard or thick over time. Corrosion tubercles or iron buildup at nodes on steel pipe (Figures 2.22 to 2.24) increase hydraulic resistance by reducing diameter and by increasing roughness of the interior surface of the pipe, dramatically increasing the energy cost to pump (Figures 2.6 and 2.32). Some well screen effects can be dramatic (Figure 2.3). In other cases, these effects may not be apparent until they are well advanced unless regular monitoring of system water quality and performance is carried out (Chapter 5). Modern turbine pumps and other pump types, such as gas-driven models, used in monitoring sampling, are robust and may not exhibit the symptoms of deterioration for long periods.

Figure 2.32 Extensively tuberculated pipe interior (Argentina: photo by Miguel A. Gariboglio).


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Likewise, significant aquifer clogging can progress before changes in well performance are noticed, such as during step-test analysis. 2.7.5.2 Sample Quality in Monitoring Wells Well deterioration can result in sample quality degradation in a number of ways. Solid material entrained in sampled water can adsorb dissolved compounds or interfere with analytical quality. Chemical encrustation reflects shifts in redox potential and pH (and sometimes pressure) that may alter the solubility of compounds in ground water. Pump and screen corrosion add metals such as Ni and Cr to ground water, where they might not occur otherwise. Corrosion also results in excessive metallic oxides in suspension. Zinc sulfides readily attach themselves to Fe sulfides. Due to the reactivity of metallic oxides such as FeIII and Mn(III-IV) hydroxides (particularly the ferrihydrite and birnassite forms), their principal effect when present is to act as chemical sieves, adsorbing reactive inorganic species and organic compounds. Pumped samples from Fe-biofouled wells and aquifers then do not provide analytical results representative of the aquifer beyond the well’s area of influence. 2.7.5.3 ASR Well Systems Most studies of aquifer storage and recovery (ASR) systems, that special class of injection wells with reversing valves so they can be transformed into pumping wells, have focused on water quality and recovery aspects. The performance of ASR wells is also potentially affected by the quality of injected water. Significant (80%) loss of specific capacity can occur within months and even weeks in aquifer formations that have limited hydraulic conductivity. Clogging of injection wells by suspended solids is a long and well-known phenomenon. Published research indicates that suspended solids tend to be the primary clogging agents in ASR systems, resulting in physical clogging. Reversing of flow (a feature of ASR wells) can cause the remobilization and deposition of fines. Likewise, incompatible water reactions (chemical reactions between injected and formation water or surfaces) can cause trouble. Some constituents can cause formation clays to swell, for example. Biological clogging is considered secondary, but (as discussed here) it is probably interactive with suspended solids in injection well clogging, and the secondary status may change with increased experience. Unless sterilized (unlikely), pretreated water will always contain microorganisms, and these will form biofilms and develop biomass in wells, regardless of the nutrient loading. Even when the injectant is chlorinated or otherwise treated with biocides, pauses between injection and pumping (as is typical with wet-season injection and dry-season pumping) result in recovery of microflora, including total coliform (TC) bacteria. So water quality alteration and injection and repumping efficiency loss are likely to be matters of ongoing concern in ASR operations. Where environmental monitoring and ASR projects are designed by personnel (environmental engineers and hydrogeologists) who usually have limited background

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in microbiology, the importance of these effects can be missed (or maybe people don’t want to know). Sometimes they have no alternatives and have to accept what happens. It is important to understand the purposes for the emphasis on bioassay in maintenance monitoring (Chapter 5) for it to be taken seriously.

2.7.6 Health Concerns Relating to Biofouling Biofouling has traditionally been considered primarily an engineering or operational concern, and not a high-priority health concern. Likewise, bioremediation is encouraged in contaminated ground water and soils, with only the use of genetically engineered microorganisms actively discouraged at present. Wherever mass growth of microorganisms is encouraged or tolerated, operators of ground-water remediation treatment systems need to consider the health aspects. 2.7.6.1 Pathogens There has been a tendency in bioremediation potential studies (although this has been changing) to pass over identification of microbial types as “too expensive.” However, if potential pathogens are present, especially in concentrated slugs in pumped ground water or aerosols from aeration towers, there is a potential hazard to personnel directly exposed. For example, Fe-precipitating and -reducing bacteria frequently found in mass microbial development include genera that are better known as including potentially enteric and respiratory pathogenic types (e.g., Escherichia, Clostridium, Klebsiella, Pseudomonas, and Serratia spp.). Mixed microbial populations in which the components produce mutually beneficial products or conditions are common in the environment. Such mutualistic consortia may contribute to the survival of other virulent or opportunistic pathogens traced to well water supplies. For example, besides the Fe-manipulating potential pathogens just discussed, Legionella pneumophila (a respiratory pathogen) is assisted by association with other bacteria. Legionella is common in soils and many other environments, including cooling tower systems that are analogous to the commonly used volatile organic carbon compound (VOC) stripping aeration towers on environmental sites. Other common sources of possible human contact are wet soils and poorly maintained water systems with dead ends and biofouling. Legionella bacteria may also be found encysted within their predators: larger bacteria and protozoa in soil and biofilms. Enhancement of natural L. pneumophila populations in natural soils undergoing aerobic bioremediation would also be expected. Wet, organically laden soils with high microbial densities are favorable habitats for their mass growth. The presence of such Legionella in airborne dust and aerosols around such remediation facilities has to be considered a potential inhalation hazard, primarily to people with impaired immune responses, including smokers, who typically lack nose and throat defenses against airborne bacterial infection.


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2.7.6.2 Toxic Accumulation Biofilms and their associated reactive metallic oxides can accumulate toxic metals and other toxics at levels higher than in the bulk ground water itself. The reason may be for some nutrient bioaccumulation purpose or as an antipredatory effect, or simply due to the reactions with the charged surfaces of metallic oxides, as previously described. The benefits of binding toxic U and Au to cell membranes and sheaths are not at all clear at this time. There have been occasions where Fe-biofouled wells were found to have become point sources of arsenic, heavy metals, and radionuclide contamination through accumulation over time. These metallic elements can originate from weathered granitic or metamorphic rocks and sedimentary rocks derived from them (such as shales), ore bodies or subeconomic roll-front deposits, or anthropogenic sources, such as buried sources of metallic or radioactive waste. Both the biofilm slug effect and microbial mobilization can result in intermittent high metal or radionuclide concentrations in the treated water. This can result in a declaration of nonperformance by the remediation site’s regulatory agency that probably would not have occurred if the biofouling were not present. 2.7.6.3 Chlorination of Organic Chemicals Chlorine and chlorine-based disinfectants (see Chapters 4 to 8) can react with components of the biofilm or hydrocarbons in the ground water to produce halogenated organic compounds. Chlorine substitutions of hydrogen make the organics more resistant to safe degradation and also more toxic. For this reason, chlorination is routinely excluded as a well treatment method for monitoring and extraction pumping wells in ground-water contamination control schemes. Chlorinated organics, forming disinfection by-products, are also an issue in public water supply.

2.8 Impacts on Treatment Plants The scope of this work does not extend to treatment plant operations and maintenance (O&M); however, it has become evident that bio-physical-chemical activity in wells (pumping and injection) has a direct influence on plant and project mission performance. Briefly, direct, adverse treatment plant effects expected should include: • Plant excessive organic loading (BOD, COD, etc.). • Sediment production and geochemical alteration of constituents so that they are not as well addressed by the treatment system. Clogging slugs of biofilm and solids (sand, silt, clay) developed out of wells may be particularly destructive to membrane and resin bed treatment systems. • Fouling of piping, sensors, air strippers, granular activated carbon columns, ultraviolet emission lamps, etc. • Alteration of geochemistry: When wells are cleaned, rapid flip-flopping of pH can be expected during treatments. Plants adapted to established reductive water may have to transiently adapt to a more oxidative Eh. Erratic

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detects or spikes of compounds whose solubility is redox or pH sensitive may occur. • Metal oxide breakthrough from filters into the rest of the treatment train: Acidic waters may flush attached iron and other metal oxides from filter particle surfaces, and breakthrough may occur, resulting in coating of downstream media and membranes. • Enhanced cost of operation due to lowered efficiencies and frequent cleaning, backwashing, or replacement of media. • Pumping well and system or aquifer clogging restricts system performance so that cleanup of calculated plume volume is slowed or stopped, or contaminated ground water bypasses the installed system while wells are replaced or rehabilitated.

2.9 Engineering and Construction Aggravation of Clogging and Corrosion Where biofouling and MIC are likely to occur, system engineering and construction can aggravate the problems they cause. For these reasons, knowledge of the potential transformations that can occur in the well-aquifer system is essential. Some aggravating human choices include: • If well development or optimal screen design is not practiced, premature clogging can be expected. Biofouling alters and clogs pore and screen slot spaces. • If corrodible metals are used, clogging with corrosion products and breakdown of the well structure can be expected. • While possibly unavoidable, the bigger the oxygenated “wash zone,” the more likely it is that problems may occur. • Pump, pressure, and valving systems can aggravate clogging within the water moving system itself. Noncompatible metals corrode, and these convoluted systems offer much surface area and small pressure changes that encourage biofouling. The design and construction of wells is not the primary focus of this book, but proper well design, construction, and development are important in prevention and planning for maintenance, as described in Chapter 4. These are areas in which engineering knowledge, skill, and application have an impact. Briefly, good well design has several interlocking aspects. Wells designed to resist corrosion, and permit reasonably free but laminar flow to the well, usually provide water with the least possible drawdown (good well efficiency), lower intake velocity at the screen, and oxidation at the intake. These are less likely to plug quickly. Good screen and filter pack selection and installation minimize potential sanding problems. The construction process can defeat a good design if packs, screens, or casings are installed in a hasty fashion or development is inadequate. Adequate development may be neglected because it takes more time and skill than may be available (or than the crews or their bosses want to spend). Project supervisors may fail to demand


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adequate development because of apparent time pressures, or they want to avoid disturbing the monitored formation. If they do not have experience with the installation of pumping wells, field supervisors may not have a grasp of the time required to fully develop a well: the scale is hours and days, not minutes. Crews in a hurry can be persuasive. Supervisors or inspectors have to stand their ground and say “keep developing!”

2.10 Well Structural Deformation and Failure: Natural and Human Caused For our purposes, our discussion of well structural failure will be confined to the casing, screen, open bedrock hole, and grout envelope. Pump and pump riser failure will be dealt with separately. We will deal with well failure based on two sources, natural and human induced. Catastrophic structural failure is relatively rare in water supply wells, where “catastrophic” infers a scenario in which the components and materials that comprise the well cease to function over a relatively short period of time (virtually instantaneously), perhaps even dramatically. Catastrophic structural failure is apparently not so rare on remediation sites. A well in which the components and materials that comprise it cease to function far earlier than the expected life span can be considered to have failed structurally, if not catastrophically. And a well that has served for decades, perhaps a century, will eventually fail structurally as the effects of time and entropy take a toll. Let’s be realistic. Total structural failure results in many of the same symptoms as in pump and casing or screen corrosion: Turbidity or sand pumping may rather suddenly increase. Yield may dramatically decline (if the pump remains functional). Related problems include pump and system wear and pump corrosion. Figure 2.33 diagramatically illustrates some examples of structural failure.

2.10.1 Natural Causes include regional forces such as tectonic (earthquakes), mass wasting (landslides and soil creep), and ground subsidence (usually resulting from overpumping). 2.10.1.1 Earthquakes Earthquakes produce complex movements in three dimensions from transverse and longitudinal (compressional) waves, as well as displacement along slippage zones. Depending on the local geology, and construction and condition of the well, effects could conceivably range from none to complete loss of the well. A well in good condition with no construction flaws would probably survive the shaking movements (vertical and horizontal accelerations) of an earthquake with no discernable structural damage, just transient turbidity. It is possible that portland cement grout would fracture due to its lack of flexibility, thus compromising the sanitary seal of

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Casing

Unstable borehole collapse

Casing collapsed due to rock fall in cavern Casing

Casing

Fault

Casing Differential force on casing from subsidence

Failure due to ground shift

Figure 2.33 Some causes of well structural failure—these are schematic representations of possible scenarios.

the well. When the well condition is not optimal, construction failures (from vertical and horizontal accelerations) may result from: • Unsupported casing in caves or due to inadequate grout support • Casing or screen corrosion and collapse—casing insufficiently strong for in-ground conditions, screen collapse due to prolonged sand pumping, and the collapse of unstable rock boreholes Open boreholes could experience temporary turbidity due to sloughing of loose or less competent lithologies (or accumulated coatings such as biofouling) from the sides. Complete loss of the well would likely result if the well intersects fractures, faults, or planes of weakness that experience physical displacement. That big reservoir of knowledge that translates to the ground-water side—the wisdom of the oil patch—gives us the example of damage to oil well casing from horizontal displacement along shale slippage planes. Casings were offset many inches with attendant plastic deformation and failure from high shock waves (rather than slow bending). It is not possible to construct well casings to withstand such forces, and the methods employed in the oil field to shield a well from displacement may not be appropriate for a potable water well. If the displacement occurred within an open borehole, the well may or may not retain its original capacity, depending on whether


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the borehole is completely occluded, and sufficient available drawdown remains visà-vis the aquifer chracteristics and required withdrawal rate. If the pump was set within or below the zone of displacement, it may be completely lost. 2.10.1.2 Mass Wasting Mass wasting is the process by which large masses of earth are moved downslope by gravity, either slowly or rapidly. Wells constructed on slopes or at the bases of slopes would be vulnerable to these processes. A slow process that may be pertinent is soil creep (Figure 2.34). Soil creep is the unsaturated downslope movement of soil, which does affect vegetation such as trees, and man-made structures such as power poles, by tilting or displacing them. It is conceivable that a well casing could at least be pushed out of plumb. Also, the sanitary grout seal may be compromised by the downslope movement of the material that surrounds it. The rapid processes include earthflows and mudflows, landslides, slump (Figure 2.35), and rockslides. Earthflows and mudflows require a degree of saturation of the materials involved. Mudflows have a higher degree of saturation and are confined within defined channels. Slump involves the displacement of a mass that rotates backwards as it moves downslope. A debris slide is the movement of a mass downslope by either sliding or rolling without backward rotation. Rockslides are masses of rock that move downslope along bedding planes, joints, or faults that are oriented (tilted) in the downslope direction. Figure 2.36 illustrates several mechanisms on a shoreline along Lake Erie that is subject to wave action erosion, slumping in the clay till, and water transport in and collapse of the overlying sand. Such forces take down trees and structures, so you can expect that a well located within the areas undergoing displacement will most likely have its casing bent out of

Figure 2.34 Slope and rail line affected by soil creep (Courtesy U.S. Geological Survey).

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Figure 2.35 Slope affected by slump (Courtesy U.S. Geological Survey).

Figure 2.36 Shoreline erosion processes, Ashtabula County, Ohio.

plumb or be displaced (Figure 2.33) or be entirely carried along with the mass. Wells located at the base of a slope that experiences one of these events have a chance of having the casing damaged or displaced by the force of impact, or to be buried. Obviously, the amount of damage that results will be event specific and may range from no damage to complete loss of the well. The authors consider it unlikely that a well could be recovered if impacted by one of these events. It would be wise not to locate wells in areas regularly subject to these processes unless no other options exist. If a well does have wet, unstable soil upslope, consider a crash revegetation program.

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2.10.2 Human Induced There is a range of structural problems that are caused by human activities. 2.10.2.1 Mining Mining, in the form of either surficial quarrying or underground pillar-and-room and long-wall extraction, can have effects on structures, including wells (Figure 2.37). More on mine blasting is found in the next section. Underground mining can have the effect of (literally) undermining overlying strata. As mass (coal, for example) is extracted, overlying strata can collapse if not supported. The practice of long-wall mining results in deliberate collapse of strata in the wake of the extraction system. Strata bend and then collapse behind the extraction face (Figure 2.38).

Figure 2.37 House foundation undermined by collapse of mining cavities (Pennsylvania Dept. of Environmental Protection photo).

Mine water breakout Coal outcrop

Sinkhole Overburden subsidence

Sandstone Underclay Through roof subsidence Coal workings

Collapse stopped Coal by strong stratum outcrop

Figure 2.38 Long-wall mining effects diagram (Pennsylvania Dept. of Environmental Protection).

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Curvature rather than vertical drop puts tensile strain on strata and structures. This is a transient effect. When vertical subsidence is approximately half of the maximum subsidence, i.e., as the face passes under the surface point, the ground reaches its maximum horizontal displacement and the strain reduces to zero again. As the long-wall face moves farther away from the surface point, the settlement continues, horizontal displacement reduces, and the ground is subjected to compressive strains. When the subsidence is complete, the ground is commonly left with no horizontal displacement and little residual tilt or strain. Most of the points on the surface will thus be subjected to three-dimensional movements, with tilt, curvature, and strain in both the transverse and longitudinal directions. The impact of subsidence on surface infrastructure is therefore dependent upon its position within the trough. The severity and duration of these impacts will depend upon the position of the point (such as a well structure) relative to each portion of the stress-strain curve. Mountaintop removal has the dual unpleasant effects of (1) literally removing aquifer rock and (2) covering and obliterating valley sediments and structures. From a hydrogeologic point of view, this is devastating on local well water sources. 2.10.2.2 Mine Blasting Significant research has been conducted into the effects of surface mine blasting on water wells (see our reading list). The impetus behind the research is the claims by domestic well owners that their wells were damaged by blasting in the vicinity of their wells. The authors themselves have received anecdotal accounts of damage to domestic wells by quarry blasting and the occasional home propane tank explosion in Ohio and oil exploration seismic shots in North Dakota, with little insight into what was experienced by the homeowner. Controlled, systematic observation of the phenomenon was needed but did not occur. No one wants to invest in it despite the benefits that could accrue. Similar to earthquakes, the forces experienced by a well during such shots appear to be vertical accelerations. Also, as with earthquakes, the severity of the impacts may be a function of the condition and construction of the well. The studies focused generally on new domestic-style wells with open-hole construction in the bedrock. In the authors’ experience, domestic wells are often of marginal integrity when new, and of very tenuous integrity to completely degraded when aged. The studies mentioned above observed no damage to casing as a result of measured accelerations of up to 2 ft/s. Counter to expectations, well performance/capacity increased as the mine wall approached the well due to stress relief increasing the porosity and permeability of the rock fracture system. Two undesirable effects were observed: temporary turbidity of the water and temporary decline in static water levels. Turbidity was attributed to drill cutting remaining in the well from incomplete development and natural deposition (Fe sulfides or oxides). Water level declines were attributed to the increase in porosity, which required some adjustment in the local flow system to reestablish static water levels. Only as the cone of depression from mine dewatering operations intersected the wells did water levels permanently decline. Municipal potable water supply wells are generally constructed to high standards and are physically robust for both sanitary integrity and long life, and most likely


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would be unaffected by blasting. Any wells with corroded, damaged, or substandard materials may expect more severe effects from blasting. The authors have observed severely corroded casing revealed in downhole television surveys. Paper-thin iron oxide remains of a well casing probably will not sustain the acceleration from blasting. The anticipated results would be the oxidized material sloughing into the well and causing significant turbidity, and the casing being open to undesirable zones in terms of both overall water quality and sanitary quality. Also possible is the fracturing of portland cement grout, compromising the sanitary seal. 2.10.2.3 Grouting The most common cause of well casing failure in the authors’ experience is related to poor or improper grouting. Well grouting is the filling of the annular space with low permeability materials that are of higher quality than those removed by the drilling process and is exhaustively described in the pertinent publications and standards that should be available to the reader who is involved in any kind of decision making about wells. Two general materials are used to grout well casing: bentonite-based grouts and neat portland cement (or portland with 2 to 6% bentonite added). Which methods for proper grout emplacement and which material to use are dependant on the specific conditions of construction and geologic conditions, and are discussed in well construction manuals, such as those listed in our suggested reading, and in ANSI NGWA-01. During construction, the well casing is grouted in place and the annular space filled (or should be filled) completely to accomplish four things: (1) provide a sanitary seal to prevent contamination from surface water, (2) prevent communication between aquifer zones, (3) provide structural support of well components, and (4) provide corrosion protection. Failure of the grout to accomplish these goals can be grouped into two issues: (1) failure to successfully emplace the grout and provide a complete grout envelope surrounding the casing and (2) choice of grout material for the specific situation. Roscoe Moss Company’s classic text (see reading list) summed up the first issue succinctly as a failure of the grouting process to completely displace the drilling fluid from the annulus, leaving channels of drilling fluid within the grout. This generalization can also include bridging in the borehole (lack of sufficient annular space) and the casing being in contact with the borehole surface (need for casing centralizers). A common mistake is drilling casing boreholes with a diameter that is too small for grout (or filter pack) to be emplaced properly around the casing. Bentonite-based grouts utilize the property of bentonite (montmorillinite) clays to swell in volume when properly hydrated. They form a somewhat firm, plastic seal around the casing as the mixture hydrates in the annular space. The swelling property ensures that the grout fills the annular space completely. Also, bentonite grout is less dense and more viscous than neat portland cement; therefore, there is less loss to the surrounding formation as a result of the high hydraulic heads at the bottom of the hole. However, bentonite grouts must remain hydrated to remain in their plastic, expanded state. Otherwise, they will shrink and crack, providing no seal around the casing. Therefore, bentonite grouts are not appropriate at sites with deep unsaturated zones. Bentonite grouts provide little to no structural support compared to neat

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portland cement. They will not support long or heavy casing strings. In the authors’ experience, bentonite grout is used in shallow constructions not much over 200 ft (60 m). It is used extensively to grout casings through unconsolidated materials overlying bedrock in open-hole bedrock wells. In this case, the weight of the casing is supported completely or partially by being seated in the bedrock prior to drilling the open-hole portion of the well. Bentonite-based grouts are vulnerable to vigorous well development and rehabilitation procedures. The authors have witnessed a pressure-acid rehabilitation job in an open-hole limestone well where the acid solution channeled to land surface through the grout, and then the pressure lifted the casing out of the hole, requiring the casing to be reseated and regrouted. Neat portland cement exhibits significant structural strength and is used in situations where heavy casing needs to be supported, formation pressures (as in artesian wells) may be encountered, vigorous physical/mechanical development may be employed, etc. It has been demonstrated to increase the collapse strength of casing after it cures in certain circumstances. It is important to choose the correct cement for the conditions and to mix it with the correct proportions of water to attain the correct strength and reduce shrinkage. It must be allowed to cure to achieve proper strength before continuing operations. Portland cement is significantly more dense than bentonite and will generate high hydrostatic pressures in deep applications. Therefore, one must be mindful of the collapse pressure of casing during grout emplacement. It can also quickly “escape” into shallow rock bedding planes or cavities, resulting in the loss of significant volumes of expensive cement. Also, the heat of hydration can be problematic, especially with plastic casing, which will soften, melt, and deform (Figure 2.39). Pure portland does shrink as it cures, which may compromise the grout’s sealing properties. Bentonite can be added to the mixture to mitigate the effects of shrinkage. Voids in the cement, as discussed above (incomplete grout envelope), will result in no enhancement of collapse strength of the casing. The purposes of using bentonite-cement grouts are a matter of controversy. We

Figure 2.39 (See color insert following page 66.) PVC casing distorted by heat due to improper cement grouting (photo by Gary L. Hix). The casing is pushed in and cracked at the visible joint and the foreground surface is blistered.


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refer you to the outside literature and ANSI NGWA-01 for more detail on this crucial aspect of well construction. 2.10.2.4 Casing Weight/Quality/Integrity/Engineering Issues Well casing performs four functions: (1) prevent collapse of borehole walls, (2) prevent the introduction of contaminants into the water source, (3) convey the water from the aquifer to the surface, and (4) provide a housing for the pump (if used). Failure of the casing to perform these functions can be grouped into two categories: (1) incorrect choice of materials/poor engineering for conditions and (2) damage to casing during handling and construction. A complete quantitative discussion of casing materials and engineering is beyond the scope of this work (and unnecessary). As with screen and filter pack design and grouting, our reading list is packed with excellent references to literature that describe casing selection and installation. In particular, the authors recommend publications by the Australian Drilling Industry Training Committee, National Ground Water Association, American Society for Civil Engineering (ASCE), and Roscoe Moss Co. In short, casing is expected to withstand the effects of corrosion, axial extension and compression, bending forces, collapse forces, and bursting forces; and it is also expected to provide a reasonable service life. Well casing is manufactured specifically for enhanced collapse and tensile strength, rather than burst strength as with line pipe. Much to the authors’ frustration, this distinction is often missed in the minds of those who write state regulations and engineering specifications. The casing must meet the rigors of rough handling during installation and years of service in the subsurface. The more extreme the subsurface conditions, the more preconstruction engineering planning should be performed to choose materials that can withstand those conditions. Angled and Horizontal Casing: Angled and horizontal or directionally installed casings have somewhat different stress, joining, and other specification issues. Neither is suspended in tension, as is the case with screened casings installed using rotary methods. Laterals of caisson-collector (e.g., Ranney collector) wells are jacked or pressed out from the caisson, and are naturally in compression. They are not hammered, as is the case with cable tool casings, but screened segments must be designed to withstand the installation process. Angled straight wells (such as those that are sometimes installed under rivers) can be subject to slight deflection depending on the straightness of the borehole and the presence of lithology with diverse compressibility. Casings in directionally drilled wells must be able to “make the turns.” Plastic (e.g., high-density polyethylene (HDPE)) is rather ideally suited for such applications; however, steel is used, as pioneered in the oil and gas industry. Such steel casing is angled in without exceeding the angular stress limits of the pipe type, wall thickness, and diameter. However, it should be recognized that the stresses imposed could be a factor in corrosion at joints. This is a specialized kind of construction that should be conducted under the supervision of engineers specializing in such applications. In the authors’ experience, the most common failures resulting from casing engineering are (1) corrosion and (2) underdesign (price trumps attention to service life).

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Premature corrosion damage is a consequence of underdesign, but it also includes the situation of the common house well, often built too fragile to clean effectively. Predominantly, casing has corroded through sooner than expected as a result of utilizing casing with too little wall thickness. No well is expected to last indefinitely, but one strives to have well replacement coincide with other changed operating conditions in the future that may require/include constructing new wells. Under the most chemically harsh conditions, alternative casing materials such as the appropriate grade of stainless steel, PVC, or composite such as fiberglass-resin would be a better choice. As states have adopted minimum casing standards (and grouting standards), this may become less of a problem. ANSI NGWA Standard 01 provides a guide. The authors have also obtained anecdotal data that some observed casing corrosion incidents are the result of periods of time when only poor-quality casing materials were available to the water well contractors. Conversely, some anecdotal observations by drilling firms with institutional memory back to the turn of the twentieth century suggest that casing steel was actually better prior to World War II in the United States. For some time, galvanized casing was sold in the marketplace, which allowed poor-quality alloys to replace better mild steel alloys. Galvanized casing is frankly a ridiculous idea, as the success of a galvanized coating depends on its uniformity. Maintaining uniformity is impossible with a pipe hammered or shoved into earth and rock, especially when threaded. Alloy choice and wall thickness (as well as a good external grout seal) are the keys to extended corrosion resistance. Good grout seals present what is effectively a single electrical grounding (earthing) potential to the casing exterior. Poor engineering for greater depths is the next cause. States adopt construction standards that normally can be expected to be appropriate for the geologic conditions and well construction practices common within their jurisdictions. As well depth increases, engineering for collapse resistance and tensile strength becomes an issue. The authors assume that collapsing or pulling apart a casing during construction is a catastrophic failure that would be immediately obvious to all involved. Scenarios in which these occur while the well is in service seem to be low-probability events and not likely to be a problem requiring diagnosis later on. However, it is conceivable that a reduction in well specific capacity with time could result in an unplanned-for pumping water level sufficiently deep to collapse the casing under some hydrogeologic and well construction scenarios. And certainly one can imagine all manner of well maintenance or repair jobs gone bad in which the casing is pulled apart and recovering tools stuck in the well. Rough handling during transportation and construction appears to increase the potential for casing failure. Surface imperfections (scratches and pits—analogous to those blemishes in galvanizing coatings) become the focus of anodic corrosion. Casing that is distorted out of round is far more susceptible to collapse. Even if correctly engineered for the expected operating conditions, postconstruction damage can occur. Development often involves violent turbulence and upward hammering by airlifted water discharge. Performance testing (a process in which we intentionally stress the capacity of the well) may result in deeper than expected pumping water levels and resultant pressure difference on the casing, resulting in casing collapse.


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Pumping at too high a pressure during displacement grouting through the casing can either balloon or burst the casing. Any procedure that requires pressurization of the casing can potentially burst the casing, and therefore must be thought out ahead of time. For example, when considering pressure acidization for well rehabilitation, gas pressure rehabilitation, fluid-pulse, or explosive performance enhancement (Chapter 8), one should consider effects on the casing, and take into consideration its weaknesses. Conversely, casing installation should be designed with such treatments in mind in the future. Most likely, casing damage from redevelopment would manifest itself as a sudden-onset water quality or turbidity/sediment problem. Among commonly used casing types, PVC casing is particularly susceptible to damage from rough handling during construction. The damage may not be apparent until it is time to install the pump or water quality degrades while in use. If portland cement grout is used, care must be taken to circulate water in and cool the casing during hydration (Figure 2.39). Heat reduces the collapse strength and the weight of the cement collapses the casing. Tripping tools in and out of the casing and rotating drilling tools could crack or puncture the casing, allowing poor quality water in. Gluing bell-end casing joints must be done with care to ensure that they are sealed properly and allowed sufficient time to set. However, if specified using National Ground Water Association guidelines and standards (and some state regulations), and installed properly, PVC casings provide a corrosion-resistant and durable installation for many purposes. Given the available experience and range of materials, the most important asset in preventing premature failure during the construction phase is knowledge. The design engineering and hydrogeology team must work together to estimate pumping water levels, exterior heads (for collapse-strength calculation) and installation and development stresses, anticipate future stresses, and estimate water quality effects. 2.10.2.5 Improper Rehabilitation and Development Methods, and Other Abuses of Wells Another category of human-induced failure is damage during development and rehabilitation. This usually involves an improper procedure for the conditions or a mistake in its application. It is closely related to damage during construction and transportation. Generally these operations involve working screen, casing, and openhole intervals with brushes, surge blocks, swabs, high-pressure jetting, and (at times) aggressive chemicals. Problems usually occur due to lack of information, application of the wrong methods (often deliberately by ignoring well cleaning specifications carefully developed by consultants), or lack of communication. Some human-induced well problems include:

1. Poor record keeping (no one knows what happened, dimensions, etc.). 2. Tools and pumps and various parts dropped into the screen or well bottom. Junk in the hole induces clogging and impairs both function and service. 3. Tools stuck and left (whistling heard from the truck window leaving the site).

We will consider this issue more completely in Chapters 7 and 8.

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Figure 2.40 Monitoring well casing bent due to vehicle collision.

Figure 2.41 PVC water well casing broken due to vehicle strike in parking lot. There was an attempt to fix it with a rubber boot coupling and protect it with a tire. This was a public water supply (bowling alley, now closed) in Ohio.

Perhaps as a final insult added to injury is vehicle damage. Vehicles are a major cause of monitoring well damage and of damage to water wells in high-traffic areas. Collisions cause casing breaks and dislocation (Figures 2.40 and 2.41). 2.10.2.6 Electrochemical Corrosion from Stray Potentials Anode corrosion is a process of which engineers and physical scientists are aware, but which really goes unaddressed when designing and constructing wells. The


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degradation of the well components starts at the anodes that are created on the surfaces of the well and spreads as cancer from there. Electromagnetic induction from high-voltage power transmission lines is a significant source of corrosion and other problems for buried pipelines. In a paper in the 2006 IEEE Transactions on Power Line Delivery, L. Bortels and coauthors reported that induced currents can be on the order of hundreds of amperes (see reading list). Pipelines are generally protected by cathodic corrosion protection systems, but in 2002, Osella and coauthors reported that the system can be overwhelmed during days of high magnetic activity. The corrosion results from pipe-to-soil potentials, with the pipe acting as an anode in the system. Wells with steel casing can be expected to be subject to the same process as pipelines if the wells are in electrical continuity with a metal waterline. As a rule, there is no electrically insulating coupling between the well and steel, copper, or ductile iron pipeline, so any induced potentials in the pipeline would also be transmitted through the well. Since both the well casing and the pump components may be in electrical continuity with the pipeline, both can be expected to be subject to the enhanced corrosion. These effects are exacerbated if the well casing pipe and screen are already damaged during handling and construction: during transport to the site, if dropped, welded, nicked during installation, etc. The most egregious damage to casing is crude slotting or perforation for water yield. Such saw- or torch-cut perforation is damaging to the structural strength of both thermoplastic and steel casing. It also provides corrosion starting points, typically anodes, in metal. This practice is the “poster child” for cheap in our field. Vertical well screens must be supported in tension during installation and never forced into place. Angled and directional well screens may be slipped in, and telescoping used for either vertical or nonvertical installations. However, excessive force and torque should be avoided. Generally, if installations follow the new ANSI/NGWA well construction standards (or even the AWWA A-100 standard) and relevant ASTM standards for materials, and proper care is observed, installations should have a chance for reasonable service life. 2.10.2.7 And Other Factors … It has sometimes been puzzling why two similar wells, both with well deterioration problems (and especially in the case of biofouling development), experience very different symptoms. The explanation may be in well design, construction, and operation in many cases, combined with subtly different in-ground conditions, such as local differences in hydraulic conductivity. These may result due to formation conditions or development differences. Such design and operational aspects are primarily in the realm that human activity affects directly, i.e., people can influence them. Toxicity and pathogenicity are also human concerns, especially for the workers operating ground-water remediation systems and people exposed to their effluents.

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Sustainable Wells: Maintenance, Problem Prevention, and Rehabilitation Immersion

Water head

Willshire, Ohio 2003 floods limestone bedrock

National Weather Service

Figure 2.42 Flooding in the St. Mary’s River watershed (Ohio) (NOAA photo).

2.11 Disaster-Related Flooding A number of catastrophic events were discussed under structural failure (Section 2.10). One that combines hydrologic and water quality effects—and is widespread— is inundation during flooding (Figure 2.42). Flooding of wells is a widespread issue in the United States, Mexico, Central America, Caribbean islands, and Bangladesh (a nation that is basically a river delta and an estuary), with the heavily populated coastal areas (and whole island nations) subject to hurricanes. A similar threat exists in the western Pacific and Indian Oceans, subject to typhoons and tropical cyclones. Much of the eastern and southern United States coastline is a flat-lying sandy landscape where wells are often very shallow and relatively unprotected from the surface. Hurricanes and intense tropical storms come ashore with large storm surges of sometimes 6 to 10 m, and generate torrential rains in short periods, causing inland as well as coastal flooding. Heavy rain events can cause river valley flooding anywhere, such as regularly occurs in the massive river basins of central North America and Europe. In North America in recent decades, major flooding events have occurred in the watersheds of the Red River of the North, and the Mississippi, Missouri, Ohio, and their tributaries. Another source of flooding in coastal areas is tsunamis. The great Indian Ocean tsunami of December 2004 (caused by plate shifting in western Indonesia) resulted in incredible devastation as far as Sri Lanka, and drownings as far as Dar es Salaam, Tanzania. This event also flooded wells with debris-laden sea water. Such flooding can inundate wells with dirty, bacteria-laden water. Of course, this is not just the occasional well, but wells over entire river basins or coastal villages, resulting in a lack of potable water for many people, and potential public health emergencies. Reflecting the structural problem discussion, inundation of wells has natural and human-generated components. The “natural” is natural meteorological and


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h ydrologic phenomena. The “human” part is the human tendency to locate dwellings and important infrastructure in areas prone to flooding. A further complication is that electric power and fuel may be unavailable, and surface infrastructure ruined (including surface-mounted pump motors, solar panels, and windmills), Thus, one of the best tools to restore a well—simply pumping off the well—is difficult to do until the capacity to pump is restored. When wells are inundated, the impact can largely be predicted using Darcy variables: hydraulic conductivity (k) and head. The head would be the height of inundation, and the k that of the shallow receiving aquifer. For the most part, debris and microbial contamination do not penetrate far into the aquifer in the well intake zone. For example, in a project the authors and Mike Vaught conducted for the NGWA and their client, it was found that extensive hurricane-related flooding in eastern North Carolina resulted in relatively little residual total coliform (TC) occurrence, even in wells one would suspect would be vulnerable to TC under normal conditions. Most of these wells were quickly pumped off after flooding when the power was restored. A larger problem in that regard is the areal impact of flushing organic carbon and contaminants into the subsurface where permeable materials extend to the surface. This can present an opportunity for enhanced microbial growth over many years.

2.12 Management and Operational Overview In addition to the construction and planning issues described above, well operation impacts biofouling in particular by providing conditions that enhance or discourage biofilm formation and buildup. Cyclical pumping or long periods of idleness, resulting in stagnation, promote biofilm formation and associated problems. Pumping beyond design capacity introduces more oxygen into the system, increasing the rate of FeII-FeIII oxidation (both abiotic and microbial) and encouraging S and Mn oxide biofouling. Such operating profiles are, of course, the operational descriptions of typical monitoring and recovery or plume control well systems and many water wells. System operational design is also a factor. In multiwell systems with automatic pump controls, stronger producing wells may produce more water to compensate for other wells with falling production. The result (in a remediation well system) may be that strong pumping occurs around productive wells, while the plume quietly bypasses clogged wells, or pumps may run, burning power for no result. There has been virtually no systemic research into these phenomena, so we just don’t know for sure. However, active facility management can make adjustments to compensate for these changes. Proactive management makes use of performance and water quality monitoring to detect such situations, and prescribes a maintenance strategy to deal with them. These topics are the subject of much of the rest of this publication.

Impacts of 3 Economic Well Deterioration 3.1 Identifying Costs of Well Deterioration We are not accountants or economists, but we are business people as well as ground-water professionals. This also is not a treatise on ground-water economics. For more on that, we refer you to the emerging body of work on that subject. Entire shelves of books have been written on this subject. A good place to start is some of the discussion in the much-anticipated International Manual of Well Hydraulics, to be published by ASCE (www.asce.org). However, we refer you to several recommended sources in the following sections (cited in our recommended reading list). We are presenting enough material here to support a discussion of the economic value of a sustainable management (maintenance and rehabilitation) of well systems (Figure 3.1).

3.1.1 Defining Economic Parameters We know that the valuation of wells and difficulties with wells are normally made in currency, although access to usable water can at times be priceless. How these valuations are calculated, and decisions about investing in prevention, maintenance, and rehabilitation depend on the questions being asked. The primary focus of our economic discussion is with the wells themselves, rather than considering resource depletion or overexploitation or similar concepts. However, as with any attempt to put a fence around parameters, the reader must realize that resource depletion does impose costs and affects well management decision making. The direct immediate costs of resource depletion at the well itself include:

1. The need to extend discharge pipe and change or modify pumps to provide service under the new conditions. 2. Depletion of aquifer thickness (reducing aquifer transmissivity), resulting in permanent decline in specific capacity. This decline can be exacerbated as shallower aquifer zones with more favorable characteristics (transmissivity, water quality) are depleted. Under certain conditions, formations may actually collapse as they are dewatered (subsidence may occur, inducing structural damage, and aquifer capacity permanently lost). 3. Increased power costs due to increased pumping lift. 4. Potentially the need to drill and construct deeper wells (land, regulatory issues and water rights, construction, etc.). 67

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Figure 3.1 The meter is running.

5. Probable decline in water quality as more recently recharged fresh water becomes less available or other change in water quality as different aquifer zones supply water to the well. 6. Related to item 5: If nitrate-rich water is drawn down to the well intake or the nitrate-reducing zone eliminated as the drawdown zone is oxidized, nitrate treatment or loss of the well as a drinking water source may become an issue. 7. Legal issues associated with depletion (neighboring water rights—however defined legally—including surface water impacts, ecological impacts, etc.). 8. Long-term economic and social uncertainty (no water, no one can live there and people move or must be relocated elsewhere, or the costs to import water are incurred).

The costs of aquifer depletion are not in the least bit theoretical, and living sustainably within the limits of local hydrologic resources obviously has economic, ecological, and social benefits. In analyzing the causes of water level decline during a wellfield performance evaluation, the degree of regional decline must be considered. If you really want to become conversant on regional water value, sustainable water extraction, and related topics, we refer you to our recommended reading list. One paper in particular is that by Emilio Custodio (2002). If you have a general interest in ground-water resources and their value, you should read more by Custodio. Our assumption is that (1) the wells in question are exploiting a renewable resource, i.e., the water pumped is being replaced by recharge, or (2) the decision maker considers depletion of a finite resource to be irrelevant, an acceptable tradeoff to achieve a goal, or beyond control. For the sake of discussion, our assumption will be that an undersirable pumping water level is due to a reversible condition such as clogging, and that investment in a solution has some probability of providing a measurable benefit (i.e., the situation is not hopeless).

Economic Impacts of Well Deterioration

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Costs of well deterioration can be divided into three realms:

1. The direct well impacts of reduced performance of the well and well equipment, such as pumps, through clogging and corrosion, including increased costs of operation through reduced efficiency 2. Increased systemwide (e.g., water utility) capital and operational costs due to corrosion, clogging, or encrustation, coating and fouling of resins, shortened filter cycles, additional chemical costs, or other need for additional treatment (e.g., for nitrates) 3. The cost of well function lost to the community or facility

The most costly result is of course the failure of the system to perform its design function, such as produce water or provide adequate monitoring of indicators of ground-water quality, plume control, or remediation. The economic valuation of wells is relatively well described technically (see our recommended reading list) but not necessarily well used in practice.

3.1.2 Types and Dimensions of Costs of Well Operation and Service As with any asset, the cost of operating a well (to be factored into cost-benefit analysis, see following) has a number of components. There is the fixed cost of the installation (construction plus planning (engineering, hydrogeology, inspection, tests, etc.) amortized over time) and operating costs (inputs of personal time, power, and other consumables). Some component of the installation cost is going to be determined by the overall degree of difficulty of the installation. How deep is the desirable water? What screen (if any) and casing diameter are needed to allow water to enter the well and be pumped away in sufficient quantity? What materials are needed? A large percentage of the direct costs of well deterioration are due to side effects of biofouling and corrosion (biological or not), such as clogging or corrosion of pumps, screens, discharge pipe, and pipelines. Costs may take the form of well rehabilitation and pump and column pipe repair or the abandonment of old wells and drilling new wells. Pumps can be particularly expensive to fix or replace, especially in developing countries. Well reconstruction after corrosion is an uncertain and costly venture to be approached cautiously. At this point in the damage assessment and decision-making process, a decision may be made on actions to deal with the deterioration. Will the well or system be operated in its impaired state? Or will it be decommissioned and replaced, or rehabilitated? Decommissioning as an option may be chosen if the system is deemed uneconomical (or otherwise not feasible) to rehabilitate. Rehabilitation may be chosen if it is technically feasible and desirable. As with the grim practice of battlefield triage, increased probability to achieve success (and confidence in success) drives the rehabilitate-or-replace equation toward rehabilitation. Rehabilitation (see Chapters 7 and 8) is usually attempted for deteriorated wells once a performance problem is recognized. Usually rehabilitation takes the form of cleaning and refurbishing pumps and mechanically/chemically cleaning the clogging and encrusting material from the well. In the case of biofouling, rehabilitation

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is often only partially successful. Relief may occasionally last for years, but more typically it lasts a few months on environmental projects. Rehabilitation of high-capacity public water supply wells, for example, is relatively costly: typically $3,500 to over $10,000 to refurbish a pump, and $500 to well over $50,000 to completely rehabilitate a high-capacity well. The cost is similar ($8,000 to $20,000 per well, regardless of the yield value) for hazardous and toxic waste recovery projects due to the usually advanced state of fouling in such wells, the extra time and care involved in the cleaning process and control of fluids, and site health and safety requirements. Purge fluids often must be handled as liquid hazardous waste and may not be suitable for treatment with the on-site process. Workers may be required to work in protective gear, and there is of course the time cost of suiting up, decontaminating people and tools, and the other well-known rituals of contamination containment. However, the alternative is an even costlier compromise or loss of well system performance or degraded water quality. An estimate of the costs of neglecting to detect and control well deterioration is warranted, even though current information is sparse. Based on a variety of available technical and economic data, one of the authors (Smith) in 1990 estimated that the direct (physical plant) cost of well deterioration for U.S. water supply utilities and irrigators is conservatively in the range of $200–285 million (1990 dollars) annually (in 2007 dollars: $314–447 million), and close to $1,000 million ($1.6 billion in 2007) when private water supply wells were included. The total economic cost to environmental control projects is not yet calculated, but easily could approach these figures, although many such pumping projects are now abandoned (see following discussion on economic valuation). Beyond the cost of replacement and rehabilitation is the cost in terms of reduced performance. For comparison, Peter Howsam and Sean Tyrrel (then of Cranfield University) estimated in 1990 that 40% of water supply wells worldwide are operating inefficiently or are out of commission due to well deterioration. Contractors performing environmental well rehabilitations are aware that the large numbers of environmental pumping wells rather quickly degrade to a less than desirable operational state. Efficiency is a large factor in pumping and other well operating costs. Helweg et al. (1983) have provided an empirical formula for calculating annual power costs.

C=

(Q)(s + SWL + h)(0.746)(T )( K ) 3956 × e

(3.1)

where C = cost in dollars per period of time (e.g., one year), Q = discharge in gallons per minute (L/s × 15.85 = gpm), s = drawdown (in feet from a static water level, SWL; m × 0.348 = ft), SWL = static water level in feet from the surface (not altitude; m × 0.348 = ft), h = system head or pressure in ft of head (m × 0.348 = ft), T = time pumped (hours), K = cost of electricity in dollars per kilowatt-hour, e = oval efficiency (wire to water) of pump and motor, 0.746 is a conversion factor for horsepower to kilowatts, and 3,956 is a conversion factor (gpm × ft) to horsepower.

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Table 3.1 Costs of Pumping (Per Year and Per Unit Volume) Cost per Year (pumping 175.2 million gal) KWh ($/kWh) $0.05 $0.09 $0.13

s=

Cost per 1,000 gal

20

45

70

KWh ($/kWh)

$10,564 $19,015 $27,467

$12,531 $22,556 $32,580

$14,497 $26,095 $37,693

$0.05 $0.09 $0.13

s=

20

45

70

$0.06 $0.10 $0.16

$0.07 $0.13 $0.19

$0.08 $0.15 $0.22

In this equation, efficiency (being in a single-variable denominator) strongly affects C. However, power cost, specific capacity, and system pressure are all important variables that can be controlled to some degree. The numerator components s + SWL + h can be simplified as total dynamic head (TDH). Table 3.1 illustrates outputs (C = $ per year and C = $ per 1,000 gal) from an example pumping 800 gpm for 10 h per day (480,000 gal/day) with SWL = 45 ft, system pressure head = 138.6 ft (60 psi*2.31), overall system efficiency = 70%, and pumping 365 days/year. Under this calculation, the single best operational action is to pick up the telephone and work power supply rates with the utility. If you can pump off-peak (e.g., at night) to shave kWh costs, you can save money (and at times, enjoy better power quality). Other critical issues include:

1. As with motor vehicle fuel efficiency, incentive to boost efficiency increases with per-kWh or per-volume-pumped cost. At 70% efficiency and $0.05/ kWh, the reduction in specific capacity (Q/s) from 40 gpm/ft (s = 20 ft) to 11.4 gpm/ft (s = 70 ft) costs $3,933/year or $0.02/1,000 gal. At $0.13/kWh, the difference is $10,226 or $0.06/1,000 gal (3.785 m3). 2. An increase in wire-to-water efficiency to 80% at $0.13/kWh and same system head saves $4,711. So buying the high-efficiency pump pays for itself rather quickly. 3. An increase in system head to 80 lb/in.2 (185 ft) at $0.13/kWh and 70% efficiency costs an additional $4,725/year, so preventing buildup in the raw water lines or filters saves money.

Note: There is an upper limit on well efficiency. This is a function of local geology; therefore, preventing efficiency decline (rather than improving efficiency)—or manipulating other variables (e.g., TDH, kWh cost)—may be the management goal. Q, s, SWL, and PWL are ultimately controlled by aquifer characteristics as the well efficiency approaches 100%. There is a limit to how much one can improve these variables, and they are specific to local aquifer parameters. Other calculations one can make using these variables can answer questions such as, “What happens if we switch pumping to well X, boosting hours pumped?” For

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example, if the companion to the example well above pumps 750 gpm and is 65% efficient, a savings could be realized if the more efficient and more productive example well is pumped for more hours, assuming that you do not incur peak-hour power rates. As we repeatedly say in our courses, “Do the math, then make a decision.” This example illustrates that relatively simple calculations of cost can be used for planning and justifying well cleaning and maintenance in pumping well applications. Such analysis is relatively theoretical. One needs to run the numbers locally. Actual savings can be higher or lower due to unexamined parameters. One example was that of the City of Madison, Wisconsin. Madison determined that its overall power usage (energy intensity) for water production was about 1.98 kWh/1,000 gal compared to 1.7 kWh/1,000 gal for comparably sized utilities, according to a University of Wisconsin study. Based on a daily average pumping rate of 33.5 million gallons, this implies about $182,000 in annual savings if the average rate could be attained. The authors of that study believed the savings potential could be significantly larger and achieved with relatively simple, proven technologies. In their case, a review of performance data revealed several key savings opportunities: (1) deep-well rehabilitation, (2) adding variable frequency drives (VFDs) and controls to distribution pumps, and (3) energy-efficient motors. If the three measures are applied across the utility, annual savings may reach 4.7 million kWh, or $256,000. In the case of well rehabilitation, percent energy efficiency improved on a ratio of 1.4:1 for each percent reduction in head. However, cost savings were even better, as pumps were also removed and refurbished to replace worn impellers. Thus, evaluation must include multiple factors. Direct economic impacts are more difficult to judge for monitoring wells. As discussed previously, monitoring wells are widely assumed to provide water quality altered by the well environment (e.g., biochemical filters). The costs come in the form of the consequences of having monitoring points providing erroneous information:

1. Questions about the validity of data in public hearings, legal proceedings, or regulatory actions, and subsequent costs of confirming data, or providing new monitoring points 2. Worse, actual arrival of a plume at a water supply well or ecological treasure because monitoring wells failed to provide the necessary early warning

It might be worthwhile to mention that now widely accepted micropurging protocols do not seem to take near-well chemical alteration into consideration, and may delay identification of monitoring well deterioration. For recovery and remediation wells, reductions in efficiency are relatively rapid and steep. Recurrence of renewed deterioration after rehabilitation is also rapid since well cleaning rarely is very effective in removing clogging precipitates. This situation puts managers of remediation wells in the position of dealing with rapid and repeated declines, with well rehabilitation in each case being relatively expensive. Although highly useful, the above operating costs equation—focused on power costs—and other equations and nomagraphs like it are relatively simple and do not address additional “downstream” factors. Examples of these include (1) increased chemical costs due to removing precipitated Fe or Mn, (2) a need for additional


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treatment (e.g., for nitrates), (3) labor and equipment costs involved in renewing biofouled water treatment systems, water treatment equipment, or encrusted pipelines, (4) excess consultant or contractor time devoted to fixing problems, and (5) business losses. Business losses to remediation or environmental engineering companies may result from reduced client or regulator confidence. Business losses for facilities may occur if regulatory officials order a shutdown if ground-water contamination is not contained. These factors have to be calculated on a site-by-site basis, using normal accounting methods (see Section 3.3). Among the important cost considerations, human time and well-being (at least ideally) stand above and beyond anything else in Western (higher-wage) economies and value systems. The costs of well materials, pumps, chemicals, etc., are relatively minor by comparison.

3.2 Asset Management and Life Cycle Cost What we are really working around here is the application of broader principles to the matter of wells and wellfields. These are assets and should rightly be considered as a part of comprehensive facility asset management and treated much as an institution would treat a fleet of vehicles or a water treatment plant. A concise and useful definition of asset management (USEPA) is that it is “a process for maintaining a desired level of customer service at the best appropriate cost.” The operating components of the definition are: • • • •

Process: Not a single action or event, that is, it is systematic. Maintaining: Not permitted to deteriorate. Desired level of … service: There is a standard of acceptable service defined. Best appropriate cost: There is a cost-benefit analysis, and cost is generally defined as a life cycle cost or per-unit cost.

Another way to look at it is that asset management is a planning process to reduce cost, and increase efficiency and reliability (finding the “best appropriate cost”) while achieving service performance and business goals. A process of asset management involves several stages or tasks:

1. Information collection: Finding out what the assets are and what condition they are in. 2. Analysis: Understanding what is critical to achieving an appropriate level of service (LOS). In conducting this analysis, it is important to ask: a. What is the facility’s or organization’s (e.g., utility) required sustained LOS? b. Which assets are critical to sustained performance? 3. Planning prioritization: This may start with prioritizing what to fix first, and may include the priority of other planned tasks. Often this process involves understanding the consequences of the failure, malfunction, or impairment of a component or system.

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4. Ongoing capital asset management: Evaluate and plan fixes and improvements that will have the best minimum life cycle cost. Ask the following questions: a. What are the facility’s best minimum life cycle cost (see Section 3.2.2), capital improvement, and operations and maintenance (O&M) strategies? b. What is the facility’s long-term financing strategy?

This process is interactive, with multiple feedback loops. Ideally, it is conducted by a team of people with multiple skill sets, and not dominated by one particular set. For example, the capital-financial management people are listening to the hydro geologists and vice versa.

3.2.1 Asset Management Features of Well Systems

1. Wells and their components have individual characteristics and likely were put into service at various times, not simultaneously. 2. They are, therefore, not going to degrade at the same rate, and they have their own features. 3. They are expensive and expected to last a long time, and they can be maintained. 4. Ideally, in any one year, maintenance is performed, with occasional replacement of major components or whole systems. 5. However, such systems (like water or wastewater treatment plants) have often been built without adequate provision for maintenance. 6. Maintenance and financial forecasting benefit from information acquisition and record keeping (budgeting is optimized). 7. There is a desirable LOS (and lack of malfunction) that requires a certain level of diagnostic and preventive maintenance action, rehabilitation and replacement, and reactive maintenance.

For ground-water systems, (1) knowing assets well, (2) understanding risks (Chapter 2), and (3) monitoring (Chapter 5) are keys to effective asset management. The budgeting (now optimized by improved data collection) for such asset management should allocate resources for the following to provide the desired LOS:

1. Diagnostics and preventive maintenance 2. Rehabilitation and replacement 3. Reactive maintenance

This desired LOS will have some quantifiable or semiquantifiable value. Experience shows that when such maintenance investment is cut, the cost is transferred elsewhere, to either tolerance of a lower level of performance, or more costly and risky incidents of more drastic rehabilitation. Defining the balance point of service value vs. inputs for maintenance requires a valuation for that desired LOS. What is the value of abundant, reliable, quality water?


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For too long, public infrastructure has been built without regard for the costs and difficulty of operations and maintenance (O&M). This is because funding and program responsibilities have been fragmented between capital and maintenance functions. Daniel Dornan, Asset Management and GASB 34—Challenge or Opportunity? Government Accounting Standards Board What is the cost of tolerating a lesser standard in your situation? If the pharmaceutical plant will leave because of the cost of self-treating deteriorating water quality, is that an acceptable cost for scrimping on maintenance costs? Can your facility obtain funding for upgrades or rehabilitation now that you collect better information? Thus is the calculus of valuing water and actions.

3.2.2 Life Cycle Costs According to the Hydraulics Institute (www1.eere.energy.gov/), the life cycle cost (LCC) of any piece of equipment is the total lifetime cost to purchase, install, operate, maintain, and dispose of that equipment. Determining LCC involves following a methodology to identify and quantify all of the components of the LCC equation. When used as a comparison tool between possible design and overhaul alternatives, the LCC process will show the most cost-effective solution within the limits of the available data. The components of a life cycle cost analysis typically include initial costs, installation and commissioning costs, energy costs, operation costs, maintenance and repair costs, downtime costs, environmental costs, and decommissioning and disposal costs. Rather than simply repeating what is written there, we direct you to the Hydraulics Institute’s publication, Pump Life Cycle Costs: LCC Analysis for Pumping Systems, available on the web. Go for it, power up the spreadsheet, and do the math. To help with the calculations, at the time of publication, there are a number of sources of present-value and LCC calculations. For example, an Excel worksheet for LCC is available from the Barringer & Associates website (http://www.barringer1. com/). Other fill-in-the-blank calculators are available. Remember that you need good data to make these efforts worthwhile. If you are the person typically likely to buy a book like ours (admittedly, not likely to become a movie script), you have a technical bent. When reading Dilbert, you identify with Dilbert or Alice, not the Pointy-Haired Boss (PHB). You think facts, argued rationally, should drive decision making (you naïve soul). You may like to sit down with a cup of coffee and develop a spreadsheet (or worksheet, if you prefer) to derive answers to questions such as “What is an LCC for this asset?” Remember that you probably have to make it understandable to those who hold your purse strings. These people are likely to be dedicated and thorough managers, but not well specialists.

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3.3 Assigning Economic Value Assigning value to ground water is notoriously subjective and often practiced in an atmosphere of misinformation. Assigning value is subjective, and representative of what a person is (subjectively) willing to pay for a good or service. It is not related to need or benefit. People pay large sums for grams of diamonds (and producers risk their lives to mine and distribute them), and diamonds are generally a useless substance in everyday use (unless you are core drilling or grinding). People buy bottled water costing up to a thousand times more than the per-liter cost of safe tap water. The health value of the bottled water is not a thousand times better (sometimes worse), plus there is an economic cost to bottle disposal and a carbon footprint issue due to transport. On the other hand, people complain about water bills when fractions of a penny per gallon bring safe water to their tap 24/7. Closer to the subject, in defining the economic value (EV) of the water in an aquifer, or an aquifer’s EV as an environmental asset, what is the appropriate value system to employ? Generally, EV is associated with water use. The EV may vary depending on how the water is used: as (among the consumptive uses) cooling water, for bottled water (as a product), as drinking water, or for irrigation (improving crop value). Quality is an issue in assigning EV. Generally, water utilities do not really charge for water itself (an extractive cost is seldom factored in) but for providing quality water (safe, palatable) in a convenient way. The customer pays for personnel time, treatment, pipes, maintenance, etc. Often these costs are undervalued in the price charged. On the other hand, affordable water is a social good: In our society (North America and the developed West generally), cheap, safe water is generally available even to the poor. In developing countries, in both urban and rural areas, water is often very expensive. In terms of labor and energy expended (hours hauling, calories expended in fuel or muscle), the per-volume cost of (sometimes unsafe, seldom treated) water in a rural village is much higher than the delivered cost of treated water in an American city. The ground water may support wetlands or other watery environmental assets that have an environmental EV (EEV) or recreational EV (REV; a subset of EEV). Such an EV is an amenity, a service function that may not be a survival function per se but improves the quality of life, for example, by providing a pleasing landscape for leisure pursuits. This definition is paraphrased from the Organisation for Economic Cooperation and Development (OECD) Glossary of Statistical Terms (www.oecd. org/). Now, there is abundant evidence that ecosystem equilibria can collapse suddenly under stress, so we have to be careful in accepting such definitions of value. Human modifications of the environment can be deadly and costly, especially in the long run. The REV of nonconsumptive in-stream flows for a single river can be tens of millions of dollars per year (e.g., recreational boating, fishing, bird watching, etc.). Additional value comes in support of endangered species (e.g., here in Ohio’s Sandusky River basin, sturgeon and bald eagles) and in making wastewater disposal relatively cheap. Thus, ground water (the source of baseflow and water in wetlands that serve as wildlife refugia) can be characterized as having an EEV.


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3.3.1 Water Supply EV In a study to define the EV of the Assiniboine Delta Aquifer in the province of Manitoba in Canada, S. N. Kulshreshtha (see recommended reading list) of the University of Saskatchewan employed a method that disaggregated the total water use into its major types, rather than picking one (e.g., irrigation) and forcing all EV analysis under that category. These categories are:

1. Municipal drinking water: Cost-of-service principle (what would be the cost of alternatives to using this water for water supply?) based on the fuzzy concept of consumer surplus—basically understanding what such a commodity is worth to people, e.g., what is the perceived worth of having abundant, good-quality water? From this valuation, a maximum cost can be established. This study further disaggregated “municipal” into residential, commercial, industrial, and other categories. 2. Rural residential drinking water: A miniature version of municipal. 3. Agricultural: Valuation compared to the water being absent for agricultural production in terms of net income change (value of irrigated crops and watersupplied livestock production vs. dryland alternatives or not producing). Such a valuation depends on crop/livestock prices, and therefore fluctuates.

The Kulshreshtha study is a valuable and replicable case history, providing a conceptual basis, the mathematics, and example calculations. Understanding the EV of the function of a well or wellfield permits the establishment of a benefit (B) to be expected from the cost (C) of a process or action (e.g., establishing a maintenance monitoring program or conducting rehabilitation). Run the numbers. Do the math.

3.3.2 Other Environmental EV While we may focus on water supply, ground water has other EEV; for example, there is a basis for EEV for:

1. Impairment of a sensitive receptor 2. Impairment as a carrier of residue

These two concepts may not seem to apply to well maintenance and rehabilitation planning. However, impairment of a sensitive receptor (e.g., a valued water asset such as a lake or a drinking water wellfield) is an inherent EV component to the benefit of maintaining monitoring and remediation well arrays. Such an impairment EV can serve as a rational valuation for defining a B to the cost of maintaining environmental well arrays. That is, the EV of the system is the EV of what would happen if it were not there and not functioning. This EV may include the cost of replacing a wellfield (land, engineering, regulatory issues, etc.) but also may include legal costs (the cost of being sued for the impairment of the asset).

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Also, some wellfields have the sole purpose of pumping water into surface water bodies. For example, the hundred-plus wells of Closed Basin wellfield maintained by the Bureau of Reclamation in southern Colorado serve to pump water into the Rio Grande in support of the multistate Rio Grande Compact. Establishing an EEV for this asset has been somewhat difficult; however, a combination of the Kulshreshtha method (summing multivariate water EV) and establishing EV for impairment as a receiver of wastewater and cooling water would seem reasonable.

3.3.3 Government Accounting Valuation of Assets In matters of diplomacy, the 1975 Helsinki Accords seemed to entrench the Cold War status quo in Europe, recognizing recognition of post–World War II borders (including Soviet claims on Baltic states). The Soviets received the recognition that they desired, while they in turn agreed to respect human rights, and acknowledge that the issue of human rights was an international concern. Soon, what became known as Helsinki Watch Groups were established throughout the Soviet Union. They became beacons that kept opposition alive in the Soviet Union. “Within 16 years, the Baltics would become independent of the Soviet Union, and full human rights would be instituted [at least for a few years] in a new Russian Federation” (HistoryCentral.com). A similar hidden asset for water and environmental infrastructure is GASB Statement 34, Basic Financial Statements—and Management’s Discussion and Analysis—for State and Local Governments, issued by the Government Accounting Standards Board (see our recommended reading list, www.gasb.org/). Again, we are not accountants, but this looks like a Helsinki Accords type instrument to sweep out the old system of paying for capital assets while neglecting maintenance funding and replacing it with an assets management valuation system. GASB 34 requires reporting the valuation of infrastructure assets and the cost of deferred maintenance. Documents referring to GASB 34 implementation seem to stall out by 2002–2003, but look for this process and imperative to be picked up again.

3.4 A Costly Example Let’s consider a fairly simple but costly example. Readers can plug in relevant costs in their own situations, and extrapolate outward for complex systems. Problem: A set of four remediation wells feeding a filter and stripper unit lose performance and clog the treatment system and piping with iron precipitation. Rehabilitation becomes necessary as abandonment is not possible. The resulting effort required: Time (never mind related direct and indirect costs): 1. A week for two people (site personnel) to take down and clean the filter/ stripper system (clogged and coated by iron precipitation), with supervision and health monitoring 2. Two days each to clean four wells plus one day each for mobilization and demobilization (contractor)


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3. Consultant time to draw up remediation plan for state approval (two days) and to confirm system and filter performance (two days) 4. Approval process triggers an OSHA site inspection, resulting in two days of managerial time, plus citations that have to be addressed Chemical/material costs: 1. Discard and replace filter media and aeration tower packing (secure disposal due to chemical residues) 2. Discard and replace accessible piping (secure disposal due to chemical residues) 3. Mechanical/acid cleaning of supply lines from wells (20 L of glycolic acid), line brush, and rods or cables (clean and test for residues) 4. Containerize and discard acid-sludge waste from lines 5. Mechanical/acid cleaning of wells, 1,000 L of glycolic acid solution, including use of a jetting rig (rig and lines to be decontaminated after well cleaning) 6. Containment and secure disposal of 3,000 L of purged pH 6.5 but turbid water containing the VOC contaminant

The goal of the following chapters is to introduce means of limiting these considerable and oftentimes unplanned operational costs. These sections include methods to compare maintenance costs vs. the costs of well deterioration.

Practices 4 Prevention for Sustainable Wells Poor performance and failure of well systems can be controlled or prevented. This can be accomplished via prevention in design and construction, recognition of well deterioration factors, monitoring for problems, and preventive actions when problems are detected. If well systems do deteriorate, a limited number of rehabilitative options are available. Monitoring and preventive design and maintenance are preferable on both cost and operational bases. Chapters 4 through 6 will consider prevention and control of well deteriorating condition, including detailed information on preventive maintenance monitoring. Rehabilitative strategies are discussed after that. If you skip ahead to “cures” (Chapters 7 and 8), come back to learn about ways to avoid a crisis the next time.

4.1 Prevention—Its Place in the Well Life Cycle There is an extensive literature and body of unpublished and uncelebrated practical experience with prevention and removal of clogging conditions in water supply wells. There is a large parallel body of experience in corrosion prevention in oil field and marine engineering systems. There is also a largely unpublished body of reports on the design, operation, and maintenance of monitoring and pumping wells on environmental sites. The quality of existing information varies greatly, and facility consultants or managers should not proceed based on armchair research alone. They should also take into account the experience now being gained by the companies and organizations that are actively performing well rehabilitation and maintenance. Based on this experience, there are several “ground truths” of well system operation and maintenance:

1. The best defense is to know about and acknowledge the presence of factors in the well and aquifer system that will cause clogging and corrosion (see Chapter 2). Knowledge can lead to either action or despair, but it will preferably lead to preventive action to the degree possible. 2. Preventive design, operation, maintenance, and rehabilitation strategies are site specific and require fine-tuning as operators gain experience with deteriorating conditions on-site. 3. Maintenance is one area where much is possible, but it requires a commitment to doing what needs to be done (Chapters 5 and 6). Maintenance is best implemented from the beginning, but can be implemented after deteriorated wells have been rehabilitated to slow or prevent recurrence of the problem. 4. Rehabilitation itself (Chapters 7 and 8) should be the last phase and last resort (before decommissioning or reconstruction) in the life cycle of a well system (Figure 4.1). It is never a permanent solution and has to be followed 81

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Well Lifecycle Continuum

Design Construct Operate Maintain Rehabilitate Jump on somewhere on the life cycle

Figure 4.1 The well life cycle continuum.

up by maintenance to be effective. Rehabilitation is frequently limited by environmental protection and safety factors when chemicals are present in the ground water. It is also limited by the typically small size and relative delicacy of some wells—including the typical domestic water well, which is usually constructed to be just robust enough so that it will not collapse. 5. In the case of environmental monitoring and treatment wells of various descriptions, prevention, rehabilitation, and maintenance possibilities are all more limited than those possible for water supply wells, and certainly those used in oil and gas production and reservoir flooding wells. The tools available for water well cleaning are receiving significant scrutiny in regulatory quarters (sometimes for good reason!). The virtuous role of prevention is limited to a degree by the need to construct wells in aquifer zones that may consist of fine sediments that are rich in microbes and diverse biogeochemical environments (see Chapter 2). Such situations can sometimes be avoided in water well design, whereas they can’t always be avoided in environmental well planning. However, performing the preventive well design at least helps to some degree in delaying performance decline and the need for rehabilitation.

4.2 Interlude: Teeth and Motor Vehicles The most instructive illustrations are those from other industries where prevention and maintenance are employed. In this regard, much of the ground-water industry remains fairly primitive in practice by comparison. Let’s look at two sectors: automobiles and dentistry. These two industries have successfully (1) cultivated a maintenance ethic in their market bases and (2) employed preventive material and design choices. If you are any older than “Boomer prime” or talk with your elders, both dentistry and automobiles are associated with much pain and inconvenience. Why most people (including your authors) remember old cars

Prevention Practices for Sustainable Wells

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with fondness is something of a mystery, and probably associated with the emotional connection we were taught to accept as children. If you are old enough (or poor enough) and remember your pre-1980s automobile (wherever it was built), you remember that it rusted. Whatever other positive characteristics it had, the holes started over the headlights, along the wheel wells, in the heater channels, etc. In my (Smith) experience, there is the neighbor’s sharplooking red 1965 Chevrolet Impala that ended life sagging in the driveway as it rotted in two (those Impala frames collected and held salty water), my 1971 Ford Pinto (seemed like a good idea!) and its four fenders in seven years, cold feet and pop-riveting plates in the 1973 Superbeetle, and the dealer driving his screwdriver through the wheel well of my 1987 Subaru wagon (I liked that car!) when I was trading it (then of course, there was its iron and copper radiator that turned to dust). You get the idea. Of course, these are all vehicles that had the misfortune of operating in Ohio. For those of you who live in warm climates, Ohio roads are salted during the winter because driving on ice and snow is hazardous. By the late 1990s, I was running steel-body vehicles for well over 120,000 mi without rust damage. Materials and design have improved. Complaints about modern vehicles are usually associated with something complex, like the automatic transmissions one cannot seem to avoid in the United States anymore. Motor vehicles really have improved (no ring jobs at 50,000 mi either). The auto industry (largely due to self-interest) also promoted preventive maintenance. We are convinced we should change oil and filters at 3,000 mi (5,000 km) intervals (even if the manual says 7,500 mi). Except for the rare individual who would rather change engines than oil (they exist), we go along gladly. This habit of maintenance preserves a major asset (a motor vehicle) and benefits the service vendor (regular service fees). If you service the vehicle at an establishment that sells vehicles, eventually the sales agent will be at the desk to convince you to trade in Old Betsy on something shiny and new. The cycle then continues. In the automotive world, the maintenance cycle involves (1) engineering to improve the product, (2) enlightened self-interest of both the vendor and customer, (3) profitability for the service provider, and (4) willing cooperation of the customer base. The history of preventive dentistry probably is more directly comparable to preventive maintenance in ground-water supply and protection. However, the ground-water industry lags about thirty years behind dentistry in this regard in North America. • Both dental and water system equipment are deteriorated by biofouling/ biocorrosion. • The mechanisms of deterioration were known in both dentistry and civil engineering by the turn of the twentieth century. Actually, the use of the toothbrush goes back centuries. • The benefits of oral hygiene were described by the end of the First World War (1918) in the United States. However, a description of the history of dentistry in North Carolina (where the first U.S. oral public health program was initiated) states that in 1934, more than half of people examined had never seen a dentist (something like what you would find now in developing countries).

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• Efforts at oral hygiene and education continued through the decades. However, toothbrushing was not practiced widely among Americans until U.S. troops brought the habit (enforced while on duty) home with them after World War II (mid-1940s). • By the 1980s, sealing children’s teeth was widely practiced, reducing the initial onset of dental decay. You get the idea. The ground-water industry was generally aware of many forms of well deterioration by the 1950s, but preventive design and treatments were limited. Stainless steel and other corrosion-resistant metals in well screens were common by the 1950s, and plastics and stainless steel were used in other critical components, especially pumps, by the 1980s. Preventive design already existed—practicing what was already recommended in the industry for well hydraulic efficiency. A resurgence of preaching the maintenance ethic in wells resumed in the early 1980s. Today, it is still viewed as a novel idea in parts of the well-using population, early in the twenty-first century. We are still at the “let them decay, then pull them and install dentures” stage in this industry (and it will stay that way as far as some are concerned), with some notable exceptions.

4.3 Prevention: Design and Construction Considerations Prevention is the fundamental step in avoiding costly and project-threatening well deterioration and plugging. As just described in reference to oral health, the best protection against deterioration in wells and water systems of any kind is prevention. Prevention involves a combination of good design and construction practices, followed by preventive maintenance monitoring and treatment. Practicing prevention requires a team effort among well managers and operators, drillers, equipment suppliers, and consultants.

4.3.1 Planning Considerations Prevention needs to start at the very beginning. Unfortunately, the usual situation at the present time is that facility operators are considering improvements in well performance after wells have deteriorated in performance or water quality. Even when reacting too late, it is useful to review good design and construction practices to assess (1) what went wrong or (2) what improvements can be made. Some problems (Table 4.1) are preventable from the beginning. A crucial part of prevention planning is proper well design and construction. There has always been a temptation on many projects to attempt to save money by asking too much of limited and undersized wells, using standard pack and screen sizes and inexpensive pumps, and shaving on development time. Considering that a well—like a set of teeth—operates bathed in a wet, biologically active, environmentally heterogeneous, and corrosive environment, good design and material choice are going to result in an optimal performance life.


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Table 4.1 General Well Design and Placement Guidelines What

Why

Room for personnel to operate and manipulate equipment around the wellhead; reasonably accessible; dry and stable wellhead area; avoid confined-space-entry conditions

Improves accuracy, and reduces the potential for accidental injury or equipment damage or loss; minimizes personnel needs for routine tasks; reduces time and equipment required for maintenance events

Locks, caps, or security apparatus are corrosion and weather resistant

Personnel do not waste time and risk injury or equipment damage attempting to perform maintenance; instrumentation is not easily damaged by heat, cold, vandalism

Water level measurement access and pumping rate readings are easily obtained

Personnel can perform these tasks efficiently and willingly

Wellhead structures and fittings permit easy removal of pumps and downhole equipment

Pumps can be removed quickly, saving money

Piping and valving designed to limit pressure drops and permit convenient flow diversion and pipe maintenance

Clogging is minimized and maintenance flushing and pigging can be accomplished to minimize total system head

Water quality taps accessible and protected from weather and corrosion

Samples can be readily obtained and taps maintained

Monitoring and recovery/control wells are no different than water wells in that quality well design and construction contribute to long and trouble-free service. For monitoring wells, quality is absolutely essential since so few effective options exist for rehabilitation. Water well, remediation well, and dewatering well system design is ably described for a variety of environments and purposes by numerous publications in our recommended reading list. The ASCE International Manual of Well Hydraulics will be an especially modern source on the subject (date of publication unknown at this point). Standards/standard practices in all these well use categories have been published by American Society for Testing and Materials (ASTM), American Water Works Association (AWWA), and National Ground Water Association (NGWA) in the United States, and by others internationally. These standards reflect modern practice in well construction and development, and many features of standards specific to certain well categories (e.g., monitoring wells) can also be transferred to other well categories. These standards are not intended to be encyclopedic, or even always highly specific. The recently developed ANSI NGWA Standard 01 is more comprehensive and detailed than the more familiar ANSI AWWA Standard A100. Combined with the specific ASTM standard guides, 01 probably should be the design framework for the ground-water industry. However, A100 is on the shelf at our regulators and referenced in their guidelines, so pay attention.

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Standards aside, design, construction, and development, of course, should be based on site-specific information—as the standards recommend. For example, even when casings, pumps, and gravel packs have been lovingly selected for material compatibility and corrosion resistance based on the literature and developing standards (using good water quality data), poor performance may still occur. For example, if biofouling is going to coat everything (blanking off a reactive casing, or alternatively, accelerating corrosion), this should be known up front.

4.3.2 Role of Well Purpose The purpose of water well construction is to provide a water supply well that will efficiently provide good-quality water over a long service life—on the order of decades. Monitoring wells, like water wells, are usually intended to have a long service life— on the order of decades. Trends in ground-water quality at a location, such as saline water infiltration, aquifer zone oxidation, or rates of plume degradation, can often only be ascertained based on long study of data from consistent monitoring points. Some monitoring wells must be ready, long after their designers are dead, to provide advanced warning of approaching problems, such as those serving as sentinels for leaking radionuclides around high-level waste repositories. Recovery and plume control wells, both examples of extraction pumping wells, have divergent lifestyles. Recovery wells, for example, are optimistically expected to have short design lives. However, current experience indicates that both recovery/ remediation and plume control are long-term processes for most sites. In any case, they must be as productive as the formation permits and do their job as long as needed. So such wells (like water supply wells) should be designed with the expectation of sustained operational life. Another difference from water supply wells for all classes of environmental wells is that they have to be in specific (often undesirable) places for the job requirement. This particular zone or aquifer has to be sampled or pumped down regardless of the longterm impact on the well. A water well (ideally) is planned and sited to abstract water from optimal aquifer zones (offering optimal yield at minimal operational risk). Quality well design and construction assists in the prevention of encrustation and corrosion problems during the life of wells. By using quality materials, care in construction, and proper sealing and disinfection, the designer and driller can help to ensure a long and less troublesome life for the well and can potentially reduce life cycle costs.

4.3.3 Well Design Proper well design, in addition to determining the depth and diameter for the purpose of the well, includes casing selection, appropriate intake section design, grouting to prevent infiltration around the casing and between sampled intervals, and procedures for well development, testing, and removal of other introduced materials (drilling fluid, surface soil, etc.). Unlike water wells, disinfection is not likely to be a necessary step in environmental wells. All of these tasks are necessary to achieve the optimal performance. Neglecting any of them is false economy.


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While monitoring and many recovery/control wells are often not great producers or efficient in a water well sense, they should still be designed with optimal efficiency in mind, within the constraints imposed by the situation (such as the need to sample specific intervals with minimum oxidation). The main reason is that designing for maximum efficiency helps to minimize biofouling and encrustation, as well as oxidation, effects to the extent possible. In monitoring well doctrine, materials selection is made so that materials do not interfere with analyses. A plus from a maintenance standpoint is that noncorrodible and nondegradable materials are also those that provide resistance to biofouling and corrosion. Table 4.1 summarizes general well design and placement guidelines.

4.3.4 Casing for Well Completion Casing is used in wells to (1) provide a stable hole and (2) seal the walls of the hole to exclude undesirable water. In a pumped well, the casing must also house and protect the pumping equipment. Casing for both monitoring and pumping wells must have (1) a sufficient diameter to accommodate pumping equipment and instruments, (2) strength to withstand forces during emplacement and use, and (3) ability to resist corrosion, heat, abrasion, and other causes of well deterioration that affect service life and mission factors, such as product or sample quality. In monitoring wells, casing diameter is often restricted to limit the amount of well purging necessary and, in some cases, to minimize the drill cuttings that have to be drummed and landfilled during well construction. In other wells, diameter is restricted due to economic considerations or limits of available well construction equipment. From a maintenance standpoint, diameter, strength, and corrosion resistance are important as well. Casings that have sufficient tensile and compressive strength and corrosion resistance are unlikely to fail catastrophically. Diameter is a factor in limiting which redevelopment tools may be used, as well as determining the volume of purge water that may need to be handled after a treatment. Casing material should be selected on a site-specific basis, taking into consideration water quality and hydrogeologic conditions. All water-well-grade casing thermoplastics have almost total corrosion resistance. However, they may be subject to attack and softening by certain organic solvents, just as if they were being solvent joined. Tetrahydrofuran, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexane, for example, if present in parts per thousand or percentage concentrations, may solvate thermoplastics. On the other hand, PVC is highly resistant to other nonpolar solvents such as gasoline components. In the typical parts per million and billion ranges of concentration, such casing degradation has not been reported. On the other hand, dissolution of cement bonds has been reported, so solvent joining should be avoided in lieu of threaded or spline-lock joints where such shallow ground-water contamination is suspected or known. Figure 4.2 illustrates bell-end and example spline-lock (CertainTeed Certa-Lok™) connectors. Numerous other types are in use. Heat is a consideration for wells on projects using heat-amended remediation, requiring cement grouting, or intended for hot-water environments. Plastics chosen (if

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(a)

OD

(b) T1 T2 L1

D

15°

BOD

L2

Figure 4.2 Some types of connections used in well casing and pump discharge pipe. (a) bell-end PVC casing pipe and (b) spline-lock coupling (Certain Teed CertaLok™).


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stainless steel is not an option) may have to be thermally stable: not likely to become reactive or to physically deform. PVC, for example, is not thermally stable above certain temperatures, depending on the composition. Thermal stability data provided by a manufacturer should be for the expected life span of the well. Short-term temperature resistance data provided may not be relevant for long-term exposure. PVC casing is at a disadvantage when mechanical cleaning is contemplated. Generally, such well casing will stand up to development forces; however, if airlifting pushes high volumes of water into the lower end of a less than optimal casing, it can break. Stainless steels have good corrosion resistance in general, but most especially if oxygen is present. The way that stainless steel corrosion resistance works is that a layer of metallic oxide is deposited on the metal surface. Under reducing conditions, however, which prevail as biodegradation of organics occurs, stainless steel corrosion resistance may be impaired. For this reason, steels of all sorts (including stainless) should be considered susceptible to corrosion under ground-water conditions in which organics are present. In a case where Type 304 may be specified under uncontaminated conditions, a higher grade, such as Type 316, may be needed. Even then, microbial corrosion is known to severely affect joints and welds in Type 316 stainless steel casing. There are many specific grades of stainless alloys. Become acquainted with them. Alternatively, plastics, at sometimes a third or less of the cost (only in materials), should be used if ground-water quality conditions will promote corrosion. However, strength and thermal considerations may preclude the use of available thermoplastics. Thermal and collapse resistance depend on the plastic pipe material used. As with steel casing, the diameter and wall thickness of the casing pipe determine the hydraulic collapse resistance of plastic pipe. Tables for various plastic and steel casings are provided in standard industry references (see our recommended reading list). The NGWA’s Manual of Water Well Construction Practices, and the ANSI NGWA 01 Water Well Construction Standard derived from it, have detailed information on both plastic and steel casing and should be in your design arsenal. Standards and data are also provided in the relevant ASTM pipe standards (American Society for Testing and Materials, West Conshohocken, PA, www.astm.org). Weld or threaded joints? The strategy is to minimize corrosion attack. How to do that depends somewhat on the application. Table 4.2 compares some casing types and materials. High-quality, uniform cement grouting provides a uniform noncorrosive barrier between steel and external environments that have varied electrochemical potentials. Bentonite grouting can serve the same purpose, but remains wet and can transmit electrical potentials. Grout sealing tends to counteract the effects of metal alterations due to welding.

4.3.5 Well Hydraulics and Efficiency—General Considerations Good hydraulic flow characteristics at the well contribute to good efficiency and reduced maintenance problems. In particular, for wells that may experience biofouling, good hydraulic efficiency reduces the impact of clogging and allows time to begin a rehabilitation program.

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Table 4.2 Casing Types and Choices Application

Casing Type

Recommendation

Water well

Mild or stainless steel

Welded joints by qualified welders, meeting industry standards; cement grouting if deep and multiple aquifers, or deep water table, bentonite grouting beneficial otherwise; if filter pack and screen, put high-solids bentonite between cement seal and filter pack

Water well

PVC

Solvent jointed if sealing is ensured before lowering; spline-lock jointing also recommended, better for deep installations; high-solids bentonite grouting

Remediation pumping well

PVC

Spline-lock jointing; bentonite grouting

Stainless steel

In case of severe corrosive and PVC-degrading conditions; welded joints above small diameter (with appropriate heat and rod types); cement grouted, but if filter pack and screen, put high-solids bentonite between cement seal and filter pack

PVC

Or exotic plastic as needed; bentonite grouted; ASTM threaded

Stainless steel (Type 316)

Where ground-water quality indicates; bentonite grouted, unless severe biocorrosion conditions indicated, then cement and separate from the intake zone by bentonite; ASTM threaded

Monitoring well

It is beyond the scope of this book to discuss well hydraulics in detail, and it is well covered elsewhere. Did we mention that you should familiarize yourself with our recommended reading list? This industry and the science and technology that go with it are too complex and diverse to be understood by oneself or by reading one slim book. You need to have references on your shelf, bookmarks in your browser, and familiarity with practice installed in your brain. However, efficient screen selection, pumping rates appropriate for hydrogeologic conditions, and thorough well development contribute to optimal hydraulic efficiency, which in turn improves the reliability of monitoring, since a good formation-well contact is established. Good well hydraulic characteristics depend on some basic understandings of the aquifer.

4.3.6 Well Screens and Intakes Wells generally can be divided into two categories, based on the intake type: screened or unscreened. Aquifer formations that require screens are usually those that are unstable, and must be held back from the borehole. These include sands and gravels as well as unstable and weathered rock formations (e.g., volcanics and their weathering products). Filter-packed screens are considered to be assumed in monitoring well design (cf. ASTM Standard Guide D 5092). Recommendations for good monitoring well screen and pack design have been ably described elsewhere (see that reading list!).


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4.3.6.1 Screen Design The ASTM Standard Guide D 5092 and water well standards ANSI/AWWA A100 and ANSI/NGWA 01 (as well as a voluminous literature) offer definitions of good screen and pack design and selection for monitoring and water wells. However, even when standards apply, it must always be realized that well design has to be site specific in nature. Screened wells in environmental applications also can be divided into those that are (1) always submerged and (2) sometimes exposed to unsaturated conditions, such as product recovery wells. In standard water well design doctrine, dewatering of the screen is to be avoided. This ideal is often not possible in dewatering wells and product recovery wells. Dewatering wells constructed over impermeable sediments or rock may have to drawdown completely to produce the desired water level. Recovery wells also often have to provide contact with the top of the local water table to permit skimming of light hydrocarbons. In these cases, engineering involves “designing for failure” more than in any other case. Designers must realize that these wells will biofoul and plug over time, design them accordingly, and make plans from the beginning to perform regular maintenance. Within the constraints of the well purpose, designing for failure can take the form of expanded filter pack and associated larger borehole diameter to permit more complete rehabilitation. Screen materials should be chosen to resist the expected rehabilitation actions. Screen inflow modification may be employed to slow velocity and clogging (see well reconstruction discussion following). Well terminuses and hookups should be designed to permit access for rehabilitation. Quality manufactured water well screens can be relatively expensive. Regardless, they are preferred for long life since they have good hydraulic efficiency. Stainless steel, plastic, and even fiberglass models resist erosion and corrosion much better than slotted steel pipe or galvanized wire screens. In any case, the slot size should be small enough to contain most filter pack particles, but not too small. The slots should be uniform in width and free of shavings or weld spatter. Various texts in our recommended reading list sources show examples of screen designs. Slotted or louvered screens should be installed with a sand filter pack per ASTM D 5092 and other literature, while wedge-wire screens may also be naturally developed under certain conditions. Screens may be installed with the casing in rotaryor auger-drilled holes, or they can be slipped inside cable-tool-driven casings using the telescoping method. 4.3.6.2 Screen and Filter Pack Material Selection With their higher surface areas, screen material selection is more critical than that for casing material. Stainless steel screens are often the material of choice for wells due to the ability to very precisely define slot size, the strength of louvered and even wire-wound screens to resist development forces, and their long-term durability. PVC or fiberglass screen made from water well casing tubing is often superior to metals under chemically reducing redox conditions in which steel corrosion is accel-

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erated. On the other hand, some solvents present may attack these materials. Also, deeper (>120 m) and hotter conditions restrict plastic and fiberglass use. In the cases where plastic screens (thermo or composite) are unsuitable due to constituents, heat, or strength factors, stainless steel should be used. However, where reduction is possible (in the presence of hydrocarbons, especially) corrosion has to then be considered in maintenance planning. One lamentable situation at present is the highly variable quality of fiberglass casing and screen products worldwide. In many cases, fiberglass composites have very favorable characteristics, with strength and heat resistance superior to those of comparable thermoplastics. However, the finish of produced items leaving exposed, friable glass fibers makes them unusable for monitoring and extraction purposes, as well as water supply production. If fiberglass is an optimal option, the quality of the available products has to be determined before specifying. It is the authors’ opinion that the use of mill- or field-slotted and perforated steel casing should be avoided in all cases, as should mild- or galvanized-steel wirewound screens, even in short-lived product recovery wells. The reason is that biofouling and biodeterioration by-products can corrode these screens well within even the optimistic estimated short performance lives. Table 4.3 illustrates the galvanic series for metal alloys. Two lists are provided, one that is general (sea water or fresh) and one for fresh water. The positions of some alloys and metals in the listing change somewhat depending on water quality and temperature. For example, zinc and iron change place above certain temperatures. Also, relative passivity or activity depends on how the alloys are treated, and may also change (as described in Chapter 2) due to manufacturing (heating and bending) and handling stress. Factory-punched louvered and wirewound screens finished and coated to minimize corrosion attack buy time against the still likely corrosion attack. In projected life spans of wells, consider: Just when has a pump-and-treat or in situ remediation project been completed on the predetermined schedule? What happens when a two-month job extends to a year and you have a screen with a two-month life span? The costs of restoring such a well or dealing with corrosion products are certainly much higher than simply specifying corrosion-resistant materials in the first place. The sand or gravel used in filter packs should be clean: free from organic soil that may cause clogging and feed bacterial growth (the native soil will be lively enough). The filter material should be as uniform as possible, with a uniformity coefficient of 2.5 or less, preferably 1.0 (ASTM D 5092), rounded (to the extent possible), and consist almost entirely of quartz. Particle size should be selected to filter the formation without silt packing at the borehole-pack interface. ASTM D 5092 specifies that the filter pack material should be selected based on sieve analysis to pass the 30% fraction (retaining 70%), and the screen should retain 90 to 99% of the pack. Again, consult ANSI NGWA Standard 01. Unscreened, open-borehole completions should include a casing or liner to the pumping water level at the least, unless (in the case of recovery wells) low specific gravity product has to be recovered at the bedrock surface or interface. Small


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Table 4.3 Cathodic-Anodic Series of Metal Alloys Protected (Passive, Cathodic, Nobler) Fresh Water Carbon (graphite) Titanium Ni-Cr-Mo-based alloys Stainless steels Copper alloys

Carbon steel/cast iron Aluminum Zinc Magnesium

General (Sea Water and Fresh Water) Gold Graphite Inconel® alloy 825 Monel Nickel 200 (passivated) Type 316 stainless steel (passivated) Type 304 stainless steel (passivated) Copper alloy (30% Ni) Red brass (85% Cu) Yellow brass (65% Cu) Type 316 stainless steel (active) Type 304 stainless steel (active) Cast iron Low-carbon steel Galvanized steel Zinc Magnesium Active (Anodic)

water-bearing fractures or screened zones above the selected pumping zone should be monitored separately and not allowed to cascade. For water supply wells, there is a trade-off between the benefit of screening multiple zones, some above the pumping water level, to extract more water or to induce flow to the well in a rock aquifer, and the challenges to well performance that the resultant cascading poses in the long run. Besides adding to water to be treated or interfering with sample quality, the water cascading down from these small seeps encourages bacterial growth and fouling. An additional issue for potable water wells is that screening shallow zones above a local water table results in more casing-seal compromises.

4.3.7 Grouting and Well Sealing In addition to basic quality well construction considerations, grouting helps by preventing the flow of bacteria-laden shallow water down into the aquifer and intake area of the well. It also helps by limiting contact of such water with the metal well casing, and thus limiting corrosion. Again, this is not essentially a manual on well sealing, but several considerations should be mentioned. Grouts should be:

1. Of low permeability (lower than the surrounding earth materials) 2. Capable of bonding well with both the casing and earth materials

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3. Capable of setting up to strength quickly to permit well completion (including development) without excessive delay 4. Chemically nonreactive with formation materials, constituents, and well materials 5. Easily mixed and pumped in a reasonable time into the annulus 6. Unlikely to penetrate far into permeable formations 7. Easily cleaned and safe to handle

The reader should stay current with developments in optimal grouting, most recently reviewed in the NGWA’s Water Well Construction Standard. Both cement and bentonite grout mixtures should be properly mixed and placed in the well so that the space between the borehole and the casing is completely sealed per evolving recommendations and standards. Unused boreholes and wells should be promptly and properly decommissioned by sealing to control inflow of oxygen and nutrients to the aquifer, which may affect fouling at other nearby wells. Note about Diameters: You need an annular space sufficiently large to permit adequate placement of grout and filter pack. Setting a casing in the next larger nominal borehole size (6 in. in 8 in.) does not allow enough room if one takes casing thickness into consideration.

4.4 Well Development Well development is the action of removing drilling damage and additives from the intake area of the well and the surrounding aquifer. We cannot emphasize enough the crucial importance of proper initial well development and redevelopment in well maintenance and rehabilitation (Chapters 6 to 8). Proper well development breaks down the compacted borehole wall, liquefies gelled mud, and moves both mud and formation fines into the well, from which they are removed by bailing or pumping. By doing so, development helps to restore the physical characteristics of the aquifer to the predrilling situation, provide a good hydraulic contact with the formation, remove fine cutting and formation material from the well vicinity, and improve stability around the well. In addition, development action in natural development situations sets up a gradation of particle sizes that tends to keep fines away from the well screen and improves permeability. Development in filter-packed wells helps to set up this gradation at the interface between the pack and the formation. Redevelopment, the process of applying physical development methods in a remedial fashion, is a crucial part of maintenance and rehabilitation treatments.

4.4.1 Reasons for Development The objective of well development for monitoring wells is to improve the ability of the well to provide representative, unbiased chemical and hydraulic data. As with pumping wells, development does this by helping to provide a suitable hydraulic con-


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nection between the well bore and the surrounding formation so that natural ground water can flow to the well, providing more accurate sample quality. Proper well development becomes more critical for wells in other ways. It minimizes the potential for damage to pumps, samplers, and sensors from abrasive particles. Those used in monitoring are often less resistant to damage than are water supply pumps. It also helps to at least initially minimize biofouling effects by removing bacteria-laden drilling mud and make-up water used in drilling, as well as contaminants such as compressor lubricating oil. By opening up the aquifer, development also helps to limit or delay the clogging impact of biofouling when it does occur. Well development methods are well described in other literature (see our reading list). These descriptions are oriented toward water wells, but most of the principles are the same as for any type of wells expected to produce some fluid. Some discussion of development of monitoring wells has taken place in the published literature. ASTM Standard D 5099 provides standard guidance for monitoring wells in granular aquifers. No such standard guidance should be considered limiting for methods used in environmental pumping wells. D 5099’s intent is to provide a minimum standard guidance for development, not to constrain methods that can be used. Standard ANSI NGWA 01 provides a state-of-the-art summary of methods and applications for pumping wells.

4.4.2 Development Method Descriptions There is a variety of development methods in use. In each case, the development of a fluid velocity in the near vicinity of the borehole is involved. Water is propelled out of the well bore and flows back in, breaking up films and mixing up the aquifer material and filter pack. There are many variations on basic approaches, and some methods are more effective than others. Preferably (and essentially in more delicate wells), the process starts gently, increases gradually in intensity, and continues as long as improvement results with a characteristic in-and-out fluid motion (Figure 4.3). One bit of information to remember is that proper well development for pumping wells takes time. It usually cannot be accomplished in half an hour, but takes some hours to fully break up drilling damage and to cause the desired sorting of formation particles. Developing just until visually clear is not enough. Another factor to remember is that not all formations can be satisfactorily developed. Wells in intervals consisting mostly of very fine particles may never develop properly, and further development may just increase turbidity. The following are descriptions of a number of conventional (pipe- and line-based) development methods that are widely employed. Monitoring and remediation well applications can employ a more limited tool kit than is available for water wells. Generally, overpumping with backflushing, surging (surge block), and jetting is employed. Application of these and other methods is discussed in Sections 4.4.3 and 4.4.4, as well as in Chapters 6 and 8.

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Reciprocating motion

Double surge block

Flow in and out of screen

Figure 4.3 The necessary in-and-out motion of proper well development.

4.4.2.1 Overpumping Overpumping (which can include bailing), a very common form of monitoring well development, brings material into the well for removal as the well is stressed by pumping. The well may be pumped at up to 1½ times the design pumping rate (if pump diameter permits), either continually or intermittently in an attempt to surge. A disadvantage of using this method alone is that overpumping and bailing, which lack the necessary in-and-out motion of optimal development actions, tend to pack formation fines against the filter pack. Conversely, backflushing packs fines against the borehole wall. These methods are not recommended for pumping well development or redevelopment. 4.4.2.2 Surging and Pumping or Bailing (Utilizing Surge Block) The surging development process is carried out by surging and bailing the well. The surging is done by a single or double solid (or valved) surge block with development water and sediment removed typically by airlift pumping. Surging should be conducted with tools capable of a 1 to 2 ft/s stroke and work the screen in 2–6 ft (1–2 m) sections, concentrating on known trouble spots. 4.4.2.2.1 Surging Mechanical surging forces water to flow into and out of the screen by operating a plunger-like surge block in an up-and-down motion in the casing (Figure 4.4). This is a highly effective method suitable for low-cost cable tool rigs. The device shown schematically in Figure 4.3 is a double surge block with capacity for pumping or


(a)

(b) Figure 4.4 Example surge blocks (both double surge block tools).

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Figure 4.5 Example well cleaning brush (manufactured by Cotey Chemical Corp., figure courtesy of Kevin McGuiness).

airlift through the central tube (see following). This is the most efficient version of the tool. A variation on the surge block is the brush (Figure 4.5). This tool, also fitting on the cable tool line, works like a bottle brush to remove incrustation and biofouling on rock walls, casings, and screen surfaces. These tools are often combined. The brush illustrated here is a commercial model that features the use of street sweeper brushes, which clean deposits without ripping hunks from casing. Variations on this theme include the line swab, which incorporates a surge block and heavy bailer that is more tight fitting than a surge block, and slowly dragged upward, then downward to clean the screen interval and casing. The flapper valve of the bailer allows the tool to fall rapidly, enhancing the surge action in the formation outside the screen. 4.4.2.2.2 Surging and Pumping Pumping is conducted through the surge block, which incorporates a piece of the suction pipe in the fabrication of the block, at rates up to half of the design capacity. A variation of surging and pumping and overpumping, especially useful in smalldiameter wells, employs a well pump moved up and down with a reversible pump puller. Upon completion of the development work, the well is cleaned to the bottom.


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Where there is insufficient submergence for airlift pumping to work properly (see following), development can proceed using surging and pumping with a well pump. 4.4.2.3 Airlift Development Airlift development is perhaps the most widely used development method for surging and pumping, especially when rotary drilling is conducted. Additionally, it can be used wherever development is needed and an air compressor can be secured. Figure 4.6 is a schematic of an airlift apparatus. Air is applied in bursts at a controlled level to initiate a surging action in the well to loosen fines and deposits. In well redevelopment during maintenance (Chapter 6) and cleaning (Chapters 7 and 8), it is very useful for mixing chemicals. When it is desired to clear the well of deposits, sand, and debris, air is applied so that the solution is driven to the surface. As the water reaches the top of the casing or floods over into the receiving tank, the air supply is suddenly shut off and the water level allowed to drop. This action is repeated as long as necessary (or budget and patience permit). Care should be taken to ensure the free flow of ground water into the screen or intake zone. 4.4.2.3.1 General Air Development Procedure The process is performed either (1) by using a single pipe air pumping system using either the casing or the borehole itself as the eductor line (casing open) or with the casing closed to the atmosphere, or (2) with a dual-line air system employing an airintroducing pipe and an air and water eductor line. Compressors, airlines, hoses, fittings, etc., should be of adequate size to pump the well by the airlift method at 1½ to 2 times the design capacity of the well. Each case is specific in terms of depth, submergence, well diameter, and screen hydraulic

Air line Plug

Educator or pumping pipe Air pipe Well casing Well screen Air pipe in position to pump Air pipe in position to back-blow

Figure 4.6 Schematic of airlift development and pumping apparatus (North Dakota State University, Scherer, 2005).

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conductivity. For wells less than 300 ft in depth, with 60% submergence possible, approximately 0.75 cubic feet per minute (cfm) of air compressor capacity is needed per gpm of anticipated pumping rate. In practice, a 375 cfm compressor developing 100 psi can usually pump 400 to 500 gpm (approximately 44 to 67 cfm) of water with proper airline submergence. 4.4.2.3.2 Development Process 1. The first goal is to establish a piston effect (surging) and not to conduct airlift pumping. In surging, sufficient air is fed to raise the water level as high as possible, then released to let it drop. 2. Airlift pumping is then used to pump the well periodically to remove sediment from the screen or borehole. When the well yields clear debris-free water, the airline is lowered to a point below the bottom of the eductor line and air introduced until the water between the eductor pipe and the casing is raised to the surface. At this time the airline is raised back up into the eductor line, causing the water to be pumped from the well through the eductor line. The procedure of alternating the relative positions of the air and eductor line is repeated until the water yielded by the well remains clear when the well is surged and backwashed by this technique. Care must be taken to ensure that air does not enter the formation, but is only used to move the fluid, which carries the kinetic development force. Under some conditions, the aquifer may become air locked when a large burst of air is injected into the screen area of the well. Aquifers with good vertical hydraulic conductivity are generally not affected by air locking. 4.4.2.4 Jetting Jetting requires a high-pressure water pump to pump fluid into the well and through jets that turn water pressure into water velocity. Return pumping can be accomplished using either an air compressor for airlift or an installed water pump. A circulation can be set up once upward pumping is initiated. When working together, the jetting and pumping set up a circulation, with the jet pumping water under pressure into the formation material, and the water returning due to the suction pumping action. This removes the foreign water and fines and drilling debris. Figure 4.7 is a jetting system schematic. The jetting tool itself can be as simple as a sealed length of pipe with drilled holes of a proper diameter and orientation (for balance) to provide sufficient volume and velocity against the screen. Figure 4.8 shows examples. Tools can theoretically be of any diameter. Small monitoring well diameters provide an engineering challenge, however, and very large tools require quite large pumps. The outside diameter of the jetting tool must be 1 in. (about 25 mm) less in diameter than the screen inside diameter. The minimum exit velocity of the jetting fluid at the jet nozzle should be 150 ft/s (45 m/s). The tool is rotated at a speed less than 1 rpm and positioned at one level for not less than 2 min and then moved to the next level, which is no more than 6 in. (150 mm) vertically from the preceding jetting level. Pumping from the well should be at a rate of 5 to 15% more than the rate at

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Air pipe Well casing High pressure water Jetting tool Water jets Well screen

Figure 4.7 Jetting system schematic (North Dakota State University Extension, Scherer, 2005).

Figure 4.8 Jetting heads (Photo courtesy of Scott Deasy, Flatwater Fleet, Inc.).

which water is introduced through the jetting tool. Water to be used for jetting must contain less than 1 ppm suspended solids. Jetting alone without pumping will agitate formation material and dislodge fines, but tends to pack debris against the borehole wall and introduces chemically altered water to the formation. The simultaneous pumping, usually by airlift, alleviates this problem. Jetting is most effective in V-slot screens and less effective in machine-slotted or louvered screens due to jet deflection, a contention supported experimentally. Jetting is also really only effective in relatively permeable formation materials and filter packs due to the limited penetration of jetting flow into the formation material. It is less beneficial than surging (see following) in rock aquifer intervals where effective permeability is provided by relatively few, discrete fractures and bedding plane partings. Any fluids introduced must be of known and acceptable quality and developed out as soon as possible. Air used for airlift must be filtered to remove any residual compressor oil. If introduction of any air or altered fluid is unacceptable, jetting is usually precluded as an option.

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4.4.3 “Conventional” Development Choices Formations monitored in environmental studies and cleanups tend to contain a high percentage of fine material, and well screens may be correspondingly fine with very limited formation contact. Rock aquifers likewise often have discrete fracture and bedding plane permeability. Surging is more easily adapted for these lowpermeability and high-percentage-fines formations than jetting, and does not require high-pressure pumping or the injection of foreign water. While jetting necessarily involves mechanical pumping, surging should also be done with power equipment, as hand surging is too hard to sustain to be effective, even with young weight-lifting graduate students on hand. The double surge-eductor pumping method version of surging helps to concentrate the surging action of the tool, and pumping brings loosened material out of the well instead of merely washing it back out on the downstroke. Such tools consist of a dual-wall pipe and double surge block (Figure 4.4). An eductor fitting is installed above the surge blocks in the pipe. Tools for this purpose are frequently driller fabricated, but commercially tools are available for small diameters (even for less than 2 in. I.D.). Prior to the use of this tool (if physically possible), material inside the casing should be vacuumed out using a suction tool. An airlift system with eductor pipe works very well. The development tool provides two actions: Gentle surging provides the agitation to remove fines in the formation-screen-pack area. A double surge block setup concentrates the surging action. The velocity of air pumped down the outer pipe and past the mouth of the eductor sets up a vacuum in the surge zone that removes water and solids (Figure 4.6). Variations on these methods are limited only by the creativity of the people employing them. Numerous tool developments combine elements of more than one method, as developers understand that multiple methods attack multiple clogging mechanisms. The best example in widespread use is the cable tool surge-eductor tool. Also, air tools have been adapted to provide a percussive force using pressure relief valves. One caution about surging or swabbing is that negative pressure should not exceed the collapse strength of the weakest well structure component (usually the screen or casing joints). For both jetting and surging with pumping, solids can be removed from effluent discharge water by settling (e.g., in a tank, which can also be used for flow rate estimation), and development water can be analyzed to monitor the well development progress. Figure 4.9 illustrates such a system in action during test drilling. This is the only objective way to evaluate well development effectiveness and to decide when to stop. Measure solids content and also check other indicative water quality parameters, such as pH, conductivity, and Eh for stabilization or evidence of changing water input (Figure 4.10), for example, new water-bearing zones encountered. Both surging and jetting should be done with considerable care, especially when developing typical monitoring, recovery, and domestic and smaller commercial wells since they are not often durably constructed (compared to many municipal water wells), are possibly deteriorated due to environmental attack, and may be more easily damaged.

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Diverter

Ope n di and scharge valv e

Tank for measuring flow rate

Figure 4.9 Airlift testing and development, test drilling in carbonate aquifer (Ohio). The illustrated system is set up to permit periodic flow testing by measuring tank fill volume over a set period of time.

Figure 4.10 Testing for field parameters during test drilling. pH, conductivity, temperature, and several key chemical parameters were measured in nonfiltered and filtered samples.

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Bailing and air surging without pumping are slow and do not permit good feedback on events downhole. Air surging alone, if overly vigorous, can also pack fines against the borehole wall and otherwise cause more damage than it solves in relatively delicate monitoring well environments. For typical monitoring and recovery well situations, two methods probably stand out as the most practical and safe for development: (1) jetting with airlift pumping and (2) double surge with airlift or eductor pumping. Both provide the in-and-out motion necessary to properly develop wells. When properly used, both provide sufficient agitation to clear fines from the formation material. Pumping clears fines from the well.

4.4.4 Fluid-Pulse Development A relatively hard-to-classify method was developed by several groups across the world, including Airburst (Frazier Industries), AirShock (ProWell Technologies, Arava, Israel), and hydropuls® (TLM GmbH, Markkleeberg, Germany). Layne Christensen’s Boreblast mark uses the AirShock system under license. These systems utilize a seismic air tool, originally developed for marine seismic signal generation. The tool releases a burst of air of a specific volume and pressure, rapidly displacing water (air displacement of 1 m in 1 ms) and generating a high-pressure percussive wave, then a negative pressure and a return flow as the air bubble collapses. The tool’s force characteristics can be calibrated infinitely over a large range by selecting tool and chamber size and air or gas pressure up to 3,000 psi. Force can rival shooting forces (up to 0.5 kg of dynamite), but the system can also be used selectively inside of well screens. More technical descriptions and illustrations are provided in Chapter 8. Hydrofracturing (injection of water and sometimes additives under high pressure) is mainly used in primary development and not redevelopment. This technique is used to open fractures and apertures, primarily in crystalline rock aquifers. A significant advantage of fluid-pulse methods is the capacity to be used in an iterative fashion, for example, “shooting” at foot or meter intervals (fired every 4–10 s) up and down a borehole interval, adjusting the tool’s characteristics in response to results (compared to shooting or other “force” methods of development, which offer a “one-shot” effort each time). Fluid-pulse methods may be used alone or in combination with chemicals and other tools. Using compressed gas or air alone is inherently low risk, and liability and legal aspects of explosives handling are avoided, as is hauling fluids. Thus, the system is highly portable as well. Cleaning projects can be relatively rapid (1–2 h). The full potential for water production can be realized only by the use of such development procedures. Water quality can be severely degraded by excessive amounts of sediment, and therefore causes unwarranted wear on pumps and increased pumping costs. Well development is not expensive in the long run, considering the improvement in yields and the elimination of sand pumping.


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4.4.5 Other Care Issues in Development and Redevelopment

1. Understand well structural limits: To avoid applying forces on the casing, screen, and grout that are beyond their capacity for resistance, care and attention to detail are required in development and redevelopment. Sufficient force, efficiently supplied, is needed to set formation particles in motion and to sheer off incrustation. However, this does not have to be a violent force that damages the well. For example, causing an excessive difference in hydrologic pressure between the outside and inside of a casing may result in casing distortion. Sharp shock loading or unloading of some well screens may cause distortion or collapse. And dislodged particles and rock fragments can break plastic casing. 2. Development typically should proceed in 3–6 ft (1–2 m) segments. 3. Tools should not impact sharply against casing joints or screen rods.

4.5 Preventing Contamination during Drilling, Well Construction, and Development Drilling and development, as well as other well intrusions such as pump service, will never be sterile or really contamination-free. On the other hand, shallow aquifers have such large microbial populations that bacteria introduced during drilling are inconsequential, anyway, in the development of well biofouling. Still, steps are available to minimize contamination from tools and limit drilling damage. One favorite tactic in water well construction in preventing microbial contamination is the liberal use of chlorination in preparing tools, treating the well during construction, and disinfecting gravel pack materials. Chlorination during monitoring and recovery well construction presents a host of problems, however, by drastically changing the aquifer environment locally and interfering with sample quality. In any case, good cleanliness practice should prevail, as a matter of quality assurance. Tools, cables, pipes, wires, etc., should be free of visible dirt, oil, grease, etc. It is a good practice to keep tools up off the soil surface and to decontaminate tools before introduction to the well. The most sure decontamination for drilling tools and components is steam cleaning. While it is not reliable for sterilization, steam cleaning at least gets the tools clean and relatively free of organic matter. These steps are normally taken in any case on monitoring and remediation well installations. There is just another reason to do so not only on environmental jobs, but on water well jobs also. Development tools, cable tool bailers, and drill tools should be handled in such a way at the surface as to minimize contamination. All equipment and material to be installed in a well that is not prewrapped and ensured clean (certainly a rare situation) must be decontaminated just prior to installation. These are not onerous procedures. This can be done by steam cleaning with an Alconox (or similar) wash and filtered water rinse, such as described sketchily in ASTM Standard Guide D 5088, followed by repeat steam cleaning to limit bacteria. However, it is important to realize that despite such measures (which will clean tools), there is no sterilization possible under any known procedure for drilling and well construction tools and equipment.

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Rant There is no technical reason why tools and pipe (casing and pump pipe) and wire cannot be kept out of the dirt on racks or on plastic, covered when not in use, and cleaned and disinfected prior to insertion. It just takes organization. Develop a site plan for a specific rig setup ahead of time. Lead driller leadership on the job site can enforce organization to make this happen. Warning: This may cut into the cell phone and cigarette time of driller helpers. If you are a contractor and routinely do this, and your competitors do not, educate your clientele to include these sanitation measures in specifications and site requirements. In spite of reservations about chlorination in environmental practice, prechlorinated water should be used for make-up water for cable tool drilling, circulation water for mud rotary, and in air injection. The water may be treated and stored in closed, disinfected tanks vented to allow chlorine to dissipate. Air used in drilling should be filtered to remove compressor oil. Simply keeping the solids contents of fluids to a minimum, minimizing the use of biodegradable polymers, and using mud tanks instead of dug pits are good practices to limit contamination. Drilling additives suppliers have made recommendations for mud control, tank designs, and chlorine levels for many years. Extensive discussion of fluids control is provided in industry publications (see our reading list— we especially recommend Drilling: The Manual of Methods, Applications, and Management). Biodegradable polymer circulating fluids and lubricating oils have some following in the monitoring well drilling field, especially for coring and directional wells, due to their capacity to break down, thus minimizing development and core interference. In the hands of experienced and skilled drillers, they have a place as long as it can be ensured that the by-products are all removed. It should be remembered, however, that the breakers used also interfere with ground-water quality, and that breakdown is seldom complete. Substrates remain that can be used by bacteria for food, and thus biofouling may be enhanced. Since biofouling interferes with sample quality, many of the advantages of polymers (relative to bentonite muds) in limiting formation interference may be negated. For any well construction method, especially those using added fluids, proper well development to remove the foreign water is both feasible and desirable. Proper development is therefore, for many reasons, a good place to start in the preventive maintenance treatment of a well.

4.6 Preventative Pump Choices and Actions Prevention should be considered in how the well is equipped and used after it is constructed. Preventative decision making begins with deliberate decisions to choose minimal-maintenance pumps and to protect them to the extent possible.


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4.6.1 Pump Selection Pump selection can be something of an afterthought for domestic water supply and remediation wells, although it is often well thought out for larger pumping wells and monitoring wells in most cases. Pump selection options have improved in recent years with the introduction of improved designs based on years of experience in the field. The pump’s service life is a definite consideration in well design and construction because of the high cost of pump repair and replacement, as well as the reliability of the installation. If a pump fails or works poorly, the well usually cannot do its job as a sampling point or means of managing a contamination plume. In general terms, pumps should be selected for good service life under the conditions that will be encountered in the wells. They should also be protected as well as possible from unnecessary environmental attack. For example, manufacturers and specifiers of well pumping equipment, as well as evolving consensus standards (most notably, the new NGWA Water Well Construction Standards), recommend that wells be thoroughly developed to limit abrasives in the pumped water (see above discussion). Screens on the pump intake may stop larger particles that may come through. Certain pump types are designed to perform under sand-pumping conditions. There is certainly a benefit to this, in that it provides a margin for error. However, sand or silt pumping is an indication of a well structural problem that should not be ignored. In extraction pumping wells in which silt intrusion cannot be fully controlled by the screen and pack, flow modification using suction flow control devices (SFCDs) or similarly engineered tail pipes has shown good results in halting or reducing it to less than 1% of the previous level. See Section 4.6.2, Ehrhardt and Pelzer (1992), and Chapters 2 and 3 in the upcoming International Manual of Well Hydraulics (ASCE, in press) in our recommended reading list. Evaluate wells individually for efficacy. Most pump types do not do well when pumping dry, especially submersible centrifugal types. In fact, submersible pumps are designed to operate within specific temperature, power quality, and intake head ranges. Output should be adjusted if necessary to avoid drawdown to the intake of the pump. Power supply and electrical protection are important considerations in keeping pumps operating. Selections in our recommended reading list describe power supply and protection considerations in detail. Also, pump manufacturer sales and specification literature should be consulted for specific pump requirements and recommendations. In any case, pump performance should be monitored and parts inspected on a regular basis. More on that is provided in the following and later sections on well maintenance and well reconstruction (Chapters 5 and 7–9). 4.6.1.1 Pumps in Water Supply and Other Extraction (or Abstraction) Wells In the past, remediation wells were simply equipped with off-the-shelf submersible well pumps designed for water wells, and this is still often the case. Such pumps are designed to pump essentially clean water at reasonable efficiency with ten- to twenty-year life cycles. Alternatively, dewatering type eductor pump systems may be employed in very shallow conditions, especially for plume control.

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Submersible well pumps have improved tremendously in service reliability in recent years. Corrodible materials have generally been replaced by noncorrodible plastics and stainless steel. Motors have improved service life, and most are directly water cooled. The general service submersible well pump is perhaps the most reliable device in the ground-water industry. Eductor pump systems have no moving parts at the pump end, relying on jet action to aspirate water upward. Water power is applied by surface-mounted centrifugal pumps. Such systems have a lengthy history of service in dewatering projects, and geotechnical engineers designing similar contamination control projects naturally employed this type of system. Still, not all such pumps do well in remediation wells. Silt, silica, carbonate scale, and excessive metallic oxides are abrasive, and quickly wear plastic impellers, seals, and bearings in centrifugal pumps. Corrosive conditions may exceed the designed limits of stainless steel components intended for use in circum-neutral pH well water. The small volute channels of submersible pumps (even those designed and priced for environmental applications) provide a flow restriction where fouling deposits tend to accumulate (sometimes in days to weeks). Until there is some design breakthrough, this will continue to be a maintenance consideration. Eductor pumps are vulnerable to clogging by metallic oxides and other solids. When water containing high levels of iron is exposed to the oxidation occurring as eductors pump air, clogging can occur rapidly. Iron biofouling can seal off eductors as well as the water circulation system very rapidly. This is a problem in shallow, organic-rich ground water even without human-caused organic contamination. Power systems are important considerations for extraction well pumps as well as those for monitoring wells. Power supply and control considerations relevant to environmental projects are discussed in detail in other literature (see the list). Power to dedicated pumps should be consistent and secure. The voltage, amperage, and phase balance should closely match the requirements of the pump. Connections should be secure and weatherproof. Control boxes should be sealed from moisture and shielded from excessive dust, sunlight, heat, and cold (not always easy on a remediation site). Cables running to wells should be routed away from heavy traffic or excavation and protected from crushing. Lines should be clearly marked and respected. On long-term projects, power systems and boxes should be vandal resistant. In potentially explosive atmosphere situations, controls should also be spark resistant, meeting relevant code standards for this purpose. 4.6.1.2 Pumps in Monitoring Wells Pumps used in monitoring may be either dedicated (installed permanently in a well and not moved) or portable (used repeatedly in different boreholes or wells). The choice is determined by the project requirements, and characteristics of these pumps are considered here from a maintenance point of view. The reader is recommended to industry literature and developing ASTM standard guides as they become available for pump selection from a sampling quality standpoint.


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4.6.1.2.1 Dedicated Monitoring Well Pumps Monitoring wells that are designed for long-term use are frequently equipped with dedicated pumping-sampling installations. These are intended to work in place for long periods, often in aggressive conditions, so their proper selection and maintenance is of interest for good service. Most of these dedicated pumps are at present of the bladder type design, with the pump at the designated pumping level, connected to the surface via discharge tubes and airlines used to transmit compressed gas to the bladder. Bladder pumps resist clogging, and the bladders generally are not subject to abrasive wear at the low flow rates used in ground-water sampling. Stainless steel submersible centrifugal pumps designed for monitoring well applications also are showing good service in silty water at least for short periods. Neither manufacturers of dedicated bladder pump units nor those manufacturing submersibles report significant maintenance problems with the pump ends in general use if abrasives are limited. However, if abrasives are present, check valves and tubing may experience scour. Most problems experienced with dedicated pumping units occur above the water level (static or pumping). Both discharge tubing and airlines, as well as their fittings, are prone to freezing in cold conditions unless protected. Provision for heaters can be made to keep the air in the well column above freezing. Wellhead fittings should be covered in any case, and can be heated also if necessary. Heated casing columns or wellheads should be vented to exhaust volatiles and humidity. Gas used for pump power in sampling pumps should be as dry as possible to limit condensation (and freezing in cold climates) in the airlines. 4.6.1.2.2 Portable Pumps and Bailers For the purposes of well maintenance planning, portable pumps transported from well to well pose different types of long-term maintenance questions. The pumps are more accessible and not exposed for long periods to corrosive water. The main maintenance concern here is service under difficult site conditions, including abusive or careless use and ease of repair and decontamination. The quality of the pumped water has to be a consideration since water containing abrasive solids can clog or wear pumps and can be difficult to clean out. Oily water may cling to pump and line surfaces and require frequent detergent washing. Mechanical matters also come into play. For pumps that are repeatedly inserted into and withdrawn from wells, it is important to pay attention to line abrasion and bending at cable or airline motor junctions. Field washing and decontamination can become a mechanical concern if deionized water freezes in the pump mechanism or lines (a problem below 20°F (–6.7°C) air temperature). In pump selection, if a particular pump type contemplated for project use is likely to become a maintenance problem, avoiding that type is step one in pump maintenance decision making. Care must also be taken with electrically powered pumps that the power supply matches the characteristics of the motor. Check connections and generator or inverter output to make sure the right volts and amps are consistently being supplied.

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Manufacturers supply detailed service and troubleshooting instructions should be read and not just filed. Besides being concerned with the pumps, it should be noted that pump insertion and extraction can also damage well casings and screens. If maintenance and reliable operation are major concerns in the project being planned, bailers dedicated to individual wells have many advantages. Bailers have no moving parts aside from balls and stopcock valves. They require no power transmission via airline or cable, and are not prone to clogging in routine use. Stopcocks and check valves may block open or closed with silt or sand. Problems then can be limited to the human operators. Difficult or slow purging, sample aeration, contamination, and other factors may weigh against bailers from a sampling viewpoint, but from a maintenance angle, they are simple and reliable in operation.

4.6.2 Pump Protection Once selected based on their characteristics and installed, steps need to be taken to protect pumps in operation (Figure 4.11). The two biggest problems are power supply and mechanical clogging and wear. Power protection involves isolation from power surges (line or lightning), including abnormal fluctuations in both voltage and amperage (which may be due to the utility supply’s weaknesses). Electrical motors should be securely grounded to an adequate, dead ground separate from the well to redirect line surges and stray currents.

Figure 4.11 Well pump electrical system protection (photo by Gary L. Hix).

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Prevention Practices for Sustainable Wells Suction flow control device (engineered tailpipe) function in a pumping well (Eucastream SFCD)

Pump jacket x x

Control element

Vh (x) + const

L??

Vh (X) = const Slots

Represents entrance velocity (proportionally to intale length)

dws db

dws db

Figure 4.12 Schematic of suction flow control device (Eucastream SFCD design, Kabelwerk Eupen AG product literature, Eufor S.A., Eupen, Belgium).

Submersible motors should be protected from running dry and all motors from running hot. If loss of submergence or flow along the submersible motor is likely, it should be equipped with sensors to cut off power if temperature or flow may vary from established norms. Use pump power protectors that cut off power if it is outside tolerances. A simple means of protecting submersible well pumps is the pump shroud, which is basically just a pipe that fits over the pump, forcing water to flow up along the motor to cool the motor as intended. Especially where screens cannot fully prevent inmigration of particles, pumps need to be protected against sand and silt pumping to limit wear. There are a number of approaches to take. Including an integral suction flow control device (SFCD) (Figure 4.12) or engineered pump intake is one option in the well intake design of pumping extraction wells that prevents sand and silt pumping, and also buys time before screen performance decline due to encrustation begins. The SFCD or engineered pump tail pipe is designed for both submersible and lineshaft turbine pumps. It extends down to the bottom of the screen, and all pumped flow is forced through it. The SFCD intake perforation profile makes it more hydraulically open at the bottom of the intake pipe than at the top. The upper part of the screen is where most flow tends to enter the screen in a conventional pumped borehole well, since the pressure is lower near the pump intake. The effect is to force a more cylindrical flow into the well (Figure 4.12).

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SFCDs have a demonstrated track record in reducing sand and turbidity, even under difficult conditions. SFCDs can also serve to reduce encrustation effects by making the entrance velocity more uniform. In some very shallow wells and in other situations where an SFCD may not be suitable (e.g., where the ratio screen length to screen diameter is less than approximately 30), available, or feasible to install, centrifugal sand separators can be mounted on the well pump to remove sand prior to entering the pump intake (Figure 4.13). How it Works

Pump enclosure shell

Submersible pump motor 1 Sandy water enters through tangential inlet slots and begins to swirl inside 2 Centrifugal action pushes sand to outer wall “Sand-free” water is drawn by the swirling vortex to the pump’s intake

4 Sand particles fall to the bottom and are purged through flexible “Flapper Valve” deep into well

Figure 4.13 Sand separator for submersible pump installation (illustration courtesy of LAKOS Separators and Filtration Systems).


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These discharge sand to the bottom of the well, but some field experience suggests that it ceases to pile up after a hydraulic equilibrium is reached. One drawback to discharging sand to the bottom in pumped wells that are monitored for quality is that particulates may hold and intermittently desorb constituents. Such accumulations can also harbor coliform bacteria and other undesirable microflora. Well design and selection is ideally the time when preventive material and process section and maintenance should start. Maintenance takes over as the operational issue once the system is constructed. This is considered next in Chapters 5 and 6.

4.7 Design Aspects: The “Cliff Notes” Version A variety of design considerations can serve to prevent or slow well system deterioration and facilitate maintenance and rehabilitation in the future. In many cases, the improvements cost little or no more than inferior designs and materials initially, and they save money in life cycle costs. Corrosion- and deterioration-resistant materials slow the deterioration of well components and limit recurrence of preventable problems, making the success of maintenance actions more likely. Specific to well equipment, PVC casing, for example, is corrosion resistant and suitable for most applications. Alternative metal casings are available where plastic or fiberglass casings are not suitable. Notable product developments that may seem new to some, but have actually been available for more than twenty years, include the widespread availability of all-stainless-steel and stainless-and-plastic pumps, high-quality rigid plastic pump discharge (drop) pipe with twist-on-twist-off or spline-lock connections (e.g., Certa-Lok), and flexible Wellmaster™ (Kidde Wellmaster) or Boreline (Hose Solutions) discharge hose (specifically designed for well pump use) composed of reliable, high-strength, corrosionresistant material that permits easy pump service. Relatively smooth pump interior surfaces and corrosion resistance increase intervals between pump service events. Pump motor and discharge-end product lines can seem to have a remarkable sameness in a competitive market. On the other hand, pumps may be marketed for environmental duty, which may not be superior to other products for aggressive ground-water pumping applications. Some considerations include:

1. Pump end material selection: a. A material designation of “stainless steel” includes a range of corrosion-resistant alloys. Some do well in anaerobic environments typical of high-organic-carbon water (e.g., Type 316 and better) and some do not (Type 304). b. Welding and stamping alters the corrosion-resistant characteristics of stainless steel alloys, so that the manufactured product may not match the resistance of the unaltered alloy. In some cases, a cast stainless bowl selection may be superior. c. While versatile, stainless steel may not suit every situation. In some high-chloride, biocorrosive environments, only high-silicon bronze or plastics may provide suitable service life.

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2. Pump end hydraulic efficiency: Higher-efficiency pump ends are recommended. Pump impeller-bowl designs and numbers of stages should be matched to the operating head conditions. 3. Achieving a balance of equipment features: Because exact matches to conditions and ideals may not be possible, pump choice may be a balance of features. In general, the highest-efficiency pump models should be used. Exceptions occur where service is so severe that short operating life spans can make more expensive, tunable pumps not cost-effective to operate. In these cases (particularly where efficiency differences are minor), low-priced but serviceable pumps that can be discarded and replaced or cleaned may be the better option.

Once selected, make provisions to protect the pump and to give it as favorable an environment as is possible, for example, installing an engineered tail pipe or SFCD, desander, or pump shroud (Sections 4.6.1 and 4.6.2). A maintenance-friendly wellhead design and completion are important to minimize the difficulty of performing maintenance. Issues include meeting limits to avoid confined space designation, making the well seal secure but removable, and making discharge head and instrument connections easy to detach. Table 4.1 provides recommendations for wellhead features to facilitate maintenance. Automated water level and pumping rate information facilitates data analysis and planning. Devices exist to provide real-time water level and discharge rate measurements without personnel being on site. SCADA (supervisory, control, and data acquisition) systems originally developed for process treatment can be adapted for well fields, permitting rapid, easy, and continuous monitoring of well and pump hydraulic performance, and even physical-chemical changes. Pump controllers help to maintain regular current flow of the proper characteristics and phase to pump motors, prolonging motor life and shielding motors from line surges. All pump motors should be equipped with automatic controllers. Two points should be kept in mind for wellhead chemical treatment:

1. Hydrants: A valved hydrant should be installed between the well pitless discharge and the well house flow meter–valve assembly for discharge to waste during treatment (Figure 4.14). Several suitable self-draining hydrant styles approved for potable water distribution are available on the market (adhering to standard ANSI/AWWA C503). During the well treatment process, a hose may be run from the blow-off hydrant to containment and treatment. 2. Systems have been developed to systematically redevelop with the pump in place, and they are designed to provide treatment chemicals to the screen where past pump-in-place designs were not effective. These should be considered as maintenance treatment options.

4.8 A Note about Well Houses Many wells (particularly in cold climates) for larger water systems feature well houses. Designs for these can be remarkably unfriendly for maintenance. At times,

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Prevention Practices for Sustainable Wells Frost-Free Blow-off Hydrant Examples (Kuperferle Foundry) Underground installation

Above ground installation

Shut off valve

Ground line

4" MJ inlet 4" FIP outlet & plug Specially depth of bury Install in meter box #7600

4" MJ inlet 4" Riser & plug Specially depth of bury #7500

Figure 4.14 Blow-off hydrant examples (photos courtesy of Kupferle Foundry Company, illustration modified).

their designs have contributed to serious injury. Besides that, they slow down work and make it awkward. Some recommendations include:

1. The roof should either (a) come off completely or (b) feature a hatch big enough to remove any well equipment (and other heavy objects in the well house). 2. There should be direct line-of-sight visibility between where a hoist crane can be set up and the top of the well casing. 3. There should be wide access into the building to permit removal of large objects. Roll-up doors are good for this. 4. If possible, make the entire structure removable. 5. The well itself can be located outside the well house, using a pitless adapter, so that pump removal and well cleaning do not involve the building at all.

Although housing another application (a wastewater plant pump station), Figure 4.15 illustrates a highly useful pump house design: big enough to house a lineshaft pump motor, valves, flow meter, and controls (and more). It can be unbolted from the pad and lifted off by the pump crane (note hoisting rings).

4.9 Well Array Design Recommendations

1. Have enough wells installed in a pumping or injection array to permit continued withdrawal operation or plume control while wells are out of service (being treated or pumps replaced).

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Figure 4.15 Example easy-to-service well house.

2. Install a ring of treatment wells around pumping or injection wells subject to clogging (where this is permitted by regulation). Example locations would be aging wellfields in which aquifer clogging is becoming significant or recovery well arrays operating in severely clogging conditions. Treatment wells can greatly improve treatment success in the near-well formation by providing a way to force treatment chemicals toward the pumping well screen from the outside, and also by providing more access for agitation of the near-well formation. One regulatory impediment in the United States is the classification by state regulators (e.g., in Ohio) of such wells as Class V injection wells. Such designation imposes licensing requirements, including fees that may make them uneconomical to install and use. 3. On sites with very deep wells, options 1 and 2 may be quite expensive. In these cases, where both replacement and rehabilitation may be very expensive and difficult, designing and planning for a rigorous maintenance defense of the existing pumping wells is especially important.

4.10 A Developing World Note As you read this, you may be sitting under a tree or near your vintage Toyota Land Cruiser, somewhere outside of North America (or maybe in your Ford F250 in a remote location on Native American land). You say, “All this is well and good for you there in the North, but we do not have all of these things. We do not even have


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well-rounded filter pack. We’re happy to have filter pack and PVC casing!” Some general principles still apply:

1. A suitable borehole diameter for grout and filter pack is more important than ever. 2. Install grout of correct proportions, mixed properly. You may need to improvise to develop a good grout using local materials, such as laterite clays that have good qualities, especially as cement is expensive in many places. 3. Choose those screen slots—regularly machine-slotted—carefully. 4. As in the old movie The Graduate, the answer is [sufficiently thick, potablewater-use, high-quality] “Plastics.” PVC and composite screens, casing, and pipe are a big help. They also can be made “in country” and are easier to transport. Maybe soon they will be made from polymers derived from materials common to the developing world. 5. Filter pack: When using a pile of pyroclastic quartzite, screen to a suitable size and wash thoroughly, then chlorinate. Bag in clean, washed agricultural bags such as used for maize or sim sim. 6. Develop more than recommended for those nice, rounded, glacially sorted quartz North American filter packs. Your hourly rate is low. 7. Use good pumps. Yes, they are expensive, but quality pays for itself. 8. Use power protection for both line power and generators. Pump off-peak for better quality. Choose three-phase pumps where possible. 9. Keep downhole components up off the ground where the cattle walk.

Monitoring 5 Maintenance Programs for Wells Once wells are designed and installed, and in operation, they must be maintained to prevent or slow deteriorating conditions. Again, if you need a cure, go ahead and make it happen, but come back here to see how to avoid a recurrence.

5.1 Maintenance Monitoring: Rationale for Instituting a Monitoring Program Once design, construction, and development are completed, well maintenance has to begin, based on a preconceived maintenance plan regularly modified to fit the installation conditions. Despite design and care in construction and development, well deterioration happens. Aquifer water quality problems on ground-water remediation projects are inevitably particularly difficult. Future problems with wells are likely to occur, and just have to be planned for and dealt with. There is a cost to preventive maintenance in operator time, contractor and consultant assistance, maintenance contracts, spare parts and equipment, analyses, and record keeping. The cost-benefit decisions on well maintenance depend on the local situation. However, studies and experience have shown the following general relationship for municipal water wells: over a twenty-year period, a program of preventive maintenance monitoring and treatment costs approximately 40% of the cost of a strategy of running a well to failure, then fixing problems. This essentially saves buying a new well. The cost of rehabilitation (the actions that bring an impaired well back to satisfactory performance) over twenty years can range from 10% to over 100% of new well construction (that is, the act of well construction alone). The high-end value can seem daunting. As discussed elsewhere (e.g., Chapters 3, 4, 7, and 8), some wells are valuable or irreplaceable where they are. Thus, investment in these tasks can be worth it. Such calculations obviously depend on the cost and difficulty of well construction in any one place, and the difficulty of the operational environment. There will be a wide range. Figure 5.1 illustrates a decision-making flowchart illustrating some of the factors involved in making rehabilitation vs. maintenance cost decisions. With smaller installations, including smaller water supply systems and monitoring and recovery well systems, the direct cost of preventive maintenance and rehabilitation is at first glance relatively more similar in cost to new construction. This is due to the relatively fixed costs of maintenance and rehabilitation that are, percentagewise, higher in relation to the cost of new construction for smaller installations.

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Sustainable Wells: Maintenance, Problem Prevention, and Rehabilitation < 85% target specific capacity

Conducts step-drawdown tests

Conduct rehabilitation Inspections: Video, tests

≥ 85% target specific capacity

Begin, continue maintenance program

With recovery comes the need to apply regular preventative maintenance with radical treatments when required

Figure 5.1 Well decision-making flowchart.

Note: In case you are unfamiliar with “smaller” ground-water extraction systems, a ground-water cleanup recovery well and a smaller water supply well serving a house, farmstead, or mobile home park greatly resemble one another. You have a 5- or 6-in. PVC casing housing an inexpensive submersible pump. In other words, they are at the lower end of the construction cost scale—not as inherently valuable as a highcapacity well system. It is important to remember that considering direct costs of various options alone can provide a distorted picture. Considering direct, immediate costs alone tends to exclude some real operational expenses (e.g., impacts on water treatment costs, such as filter backwashing) and also the implications of future problems temporarily avoided. For example, rehabilitation and new construction involve the personnel expense of submitting rehabilitation plans or new designs to the authorities, the meetings, the questions, etc. Maintenance minimizes the need for such planning work, especially if the maintenance plan is part of the initial facilities plan. Maintenance flies under the regulatory radar, and evidence of it builds confidence in your credibility. New well construction may simply serve to temporarily avoid recurrence of a problem. Current experience is demonstrating that clogging, biofouling, and Fe/Mn/S transformations may extend several meters away from existing problem wells. Wellfields in operation for several decades likely have a subsurface environment prone to biofouling covering the entire area of the asset. The need to control or monitor plumes usually constrains where new wells can be placed. Of necessity, a replacement well must operate in the same challenging locations as the abandoned problem well, and subsequently fall rapidly to the same symptoms. Do not have any illusions about a new well installed near abandoned clogged wells. The symptoms will recur sooner or later—assume sooner. Well maintenance is therefore the better option than abandonment and new construction when existing well systems are well designed and constructed, because the old problem cannot be easily avoided. Where existing failing wells are not up to current standards and are tagged for abandonment, the performance problem of the former wells cannot be considered solved by installing new wells. Well deterioration that is no less aggressive than the old problem will recur with the new wells unless a maintenance program is implemented.

Maintenance Monitoring Programs for Wells

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Finally, regardless of comparative costs, you should consider the question, “What is the value of smooth operation (a reliable level of service (LOS)—Section 3.2) to your facility?” when making management decisions about maintenance. This is what is known as an externality— it has value, but this value can be subjective, although it can and should be quantified as discussed in Chapter 3. As in the operation of any engineered system (e.g., trucks or nuclear power plants), maintenance of monitoring and remediation well arrays and their attached systems preserves valuable assets and keeps them up and running. Preventive maintenance, even if the costs are high, are budgeted items and scheduled events. Well rehabilitation, by contrast, is conducted under emergency circumstances, is never convenient, and was probably not in the budget. The collective act of systematic tracking, assessment, and maintenance of systems is now lumped under the term asset management (Section 3.2). A choice in favor of intentional well maintenance is simply a decision to consider well systems to be genuine physical assets, just like a fleet of trucks or a water treatment plant, part of asset management rather than throwaway items or mere “holes in the ground.” They are extensions of your facility that happen to be underground. Management systems of engineering companies consider regular cost control and regular preventive maintenance as part of the cost of operating physical assets. In the case of a household or community water supply, that well is a drinking water source and who wants to tolerate a deteriorating, nasty water source? The principles are otherwise precisely the same for wells as for other mechanical assets that are expected to work without much attention in a hostile environment: none works well if it is neglected. Like vehicles and wastewater plants, well systems are more expensive to fix and replace than to maintain properly over their life cycles (Section 3.1.2). Strategies that result in premature replacement of wells and associated systems, such as pumps, drive up system life cycle cost (LCC). Unlike vehicles and wastewater plants (and more like underground storage tanks), problems with wells are not visibly apparent. Rational, systematic well maintenance is, however, entirely possible. Routine well maintenance as envisioned here has a short modern engineering history, but where systematic maintenance inspection, monitoring, and treatment have been employed, they have visibly reduced clogging and other impacts on well performance, piping, and filtration and treatment equipment.

Maintenance, Stewardship, Husbandry, and Other Value Judgments We get caught in our “silos” of various industries and disciplines, where we do not look at the examples of others. The asset management industry is productive to mine for techniques, and the maintenance ethic we are preaching here is analogous to land stewardship or husbandry in agriculture. If you take care of the land, it takes care of you. This is a sustainable system (sustainable is in the title of this book).

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5.2 Maintenance Procedures Overview Wells are best maintained by a preventive maintenance program that involves a combination of regular monitoring of their physical condition and well performance factors, and reconstructive maintenance and preventive treatments as necessary. Maintenance monitoring is monitoring of well physical, hydraulic, and water quality factors for the purpose of detecting deterioration conditions. Reconstructive maintenance is replacement of well and pump components on an as-needed or scheduled basis. Preventive treatments are redevelopment or chemical treatments applied before significant, irreversible performance decline occurs, often on a schedule once the rate of corrosion, biofouling, etc., is known. Rehabilitation is the next resort when a well’s performance is allowed to deteriorate too far. The last step is abandonment and starting over. If well failure and replacement has had to happen in the course of events, then the well system manager has a chance to “get religion,” implementing a maintenance program to prevent or delay a recurrence.

5.3 Implementing a Maintenance Program— It’s Institutional, Not Personal The primary task in a preventive maintenance program is first of all to make the institutional commitment to perform preventive maintenance on wells, assuming that well deterioration is a potentially serious and costly problem. It is hoped that the case for this assumption has been amply made here. The commitment has to be institutional and not the personal mission of one facilities manager, who may die, retire, storm off in disgust, divorce the boss, or otherwise move on next month, although it typically starts that way. One individual has a vision (based on possibly bitter experience) that a preventive maintenance program is needed. That person influences others with this worldview. If it remains the personal commitment of one person only, the momentum toward a maintenance program is lost in the transition until the next manager encounters a crisis.

5.4 Maintenance Is Personal (and Personnel), Too Experience shows that the combined sensory-analytical systems of animals (including humans) often outperform physical-electronic instruments. Humans working with critical systems (cavalry horse, steam engine, turbine, well pump) develop sensitivity to subtle behaviors and sounds of that system and are able to detect if there has been a change in the system. Most of us are familiar with being in tune with our motor vehicles. Is there a new squeak? Greater roll and sway during cornering? A rapid tick when accelerating uphill? We know these sounds are warnings. Engine tuning by ear used to be an important mechanic’s art, but is now less important due to the dominance of electronic controls on newer vehicles. Relative to wells, pump wear and line clogging result in changes in sound during pumping. Increased drawdown may be detected due to cascading or a change in the


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sound of recovery. Women at village wells know when the pump foot valve is worn: It takes longer and more strokes for water to come to the surface! The jugs and buckets line up longer and longer. The human mind can also make leaps of logic, often referred to as intuition, about conditions based on such sensory input. The trained operator will make such a deduction, follow it up with some confirmatory measurement, and document the issue. Such deductions are more likely to be valid if the person is better informed. Having a trained and equipped person around who is familiar with the wells operated by a facility makes use of these talents and capabilities. Such capability takes time, so nurturing and maintaining staff for long periods is important. Longevity alone is not sufficient. They person has to listen and feel, too. This means that the person has to care. What if we developed dogs trained to use their sensory capabilities to detect biofouling in its early stages? Resistance: The following is going to require some hands-on attention and effort. However, people (especially North American private well owners, who rely on the well water being a pure water source) resist doing maintenance testing, inspection, and record keeping. Then they are upset when deterioration happens. It is time for the ground-water industry, water supply, and health oversight sectors to insist maintenance efforts must be performed.

5.5 Maintenance Basics As in any kind of maintenance, well maintenance includes some simple asset-protecting activities. Among these are simply knowing where wells are, making sure they are accessible and visible, making sure records are kept and available (and not buried in a file cabinet at some off-site office), and checking on their surface equipment. Are the caps on? Are the locks working? Are the well tops visible and properly labeled? Are their well construction (as built) records available? Do pumps operate within nominal ranges?

5.5.1 Well System Maintenance Records Well records are among the most valuable tools in well maintenance because they provide the necessary dimensions and history to make maintenance and rehabilitation effective. Without records, maintenance and rehabilitation are much less certain of success, and more prone to failure. In addition to construction data, the maintenance system should have an accurate record of well operational information and data, such as water quality, recorded over time. These records should be organized in a logical fashion within the framework of the facility’s management system, and readily accessible to people in the organization concerned with well maintenance (but not to just anyone, for security reasons). Such a record system may consist solely of hard-copy paper files or may include a database spreadsheet system, such as is presumably available and familiar to the vast majority of managers of monitoring and remediation programs. Ideally, the computerized system speeds data retrieval and analysis (if designed and used properly).

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We are not living out a Dilbert cartoon, are we? Specific well system management software is available (but must be modified to exactly fit a certain facility’s needs). Business type spreadsheet database software may suffice (often combined with geographic information systems (GIS)), and can be adapted by a knowledgeable team of computer and water well people to fit the well maintenance needs of the facility. Computer systems should be securely backed up—preferably off-site—and augmented by hard-copy or image (e.g., pdf, jpg) files of existing hard-copy documents, such as well logs, invoices for services, and test results. In actuality, critical summary information (existing equipment, pump setting, discharge rates, capacities, water quality, water levels, etc.) should be kept in hard copy, printed on acid-free paper in a secure place in fireproof files. Copies of video tapes and disks should be made and stored securely as well. You know, even one hundred years is not a long time. It is important that maintenance records be available to all the relevant parties on a need-to-know basis. Facility managers and owners should have contractual access to records maintained by contractor management and well maintenance firms in case of changes in contracting firms (hardly an unusual occurrence). These files remain the property of the facility’s owners (not the contractor). In the case of environmental cleanup sites, the site’s responsible party also must have access.

5.5.2 Maintenance Monitoring for Performance and Water Quality Maintenance monitoring is the process of performing systematic monitoring to permit early detection of deterioration that may affect the well’s hydraulic performance and water quality. The ideal is to detect deteriorating effects in time to prevent problems or allow the easiest possible treatment. Without collecting quantitative data, symptoms of well deterioration may not be apparent until well performance is severely impaired. The results of system water and quality and performance monitoring are compared over time to establish trends. Such problems can be prevented and mitigated by effective O&M, but to do so requires valid information on the environment, hydrology, and material performance of the well system produced by information collection in the process known as maintenance monitoring. Table 5.1 is a testing summary guide and Table 5.2 summarizes factors of interest in maintenance monitoring. In general, maintenance monitoring approaches should be tried and reviewed over a period of time and adjusted based on experience. Systems and procedures must be implemented as part of a systematic maintenance program involving: • • • •

Institutional commitment A goal of deterioration prevention Systematic monitoring as part of site maintenance procedures A method evaluation of information to determine what maintenance actions are necessary

In any case, it has to be recognized that monitoring approaches and responses will be site specific, and likely will require adjustment during implementation.

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•

Silt/clay infiltration

•

•

•

•

•

•

•

Pumping water level decline

•

•

Lower (or insufficient) yield

•

•

Complete loss of production

•

•

•

•

•

•

•

•

•

•

•

•

•

•

•

Chemical encrustation

•

Biofouling plugging

•

Pump/well corrosion

•

•

•

Well structural failure

•

•

•

•

Check for Power Malfunction

•

Test Pump Mechanical Condition and Performance and Changes in Head Relationships

Conduct Step Tests and Review History

•

Test for Physical-Chemical Parameters and Review Records

Check SWL and PWL and Review Histories

•

Test for biofouling Parameters and Review Records

Conduct Downhole TV Inspection

Sand/silt pumping

Problem

Review Area-Regional Ground-Water Conditions

Review Design and Construction Records

Table 5.1 Troubleshooting Summary Guide for Well Maintenance

•

•

•

•

•

•

Source: Modified from Borch et al. (1993) and Smith (1995).

Timescale note: Over the eighty-year life span of a well, the first twenty years may reveal the trends and correlations/relationships that inform the next sixty years of maintenance activities. Think lifetime, not next fiscal cycle.

5.5.3 Maintenance Actions and Treatments Once maintenance or diagnostic testing has indicated that a deteriorating condition is likely to cause a problem, or has established a suitable maintenance interval, some action needs to be taken. This may be in the form of an inspection and repair of a component such as a pump, replacement or cleaning of a filter, or some treatment

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Table 5.2 Parameters Useful in Well Maintenance Monitoring Hydraulic testing

Pumping rate and drawdown for specific capacity (acceptance rate and WL rise in injection wells) Total amount of pumping time and quantity pumped per year Periodic step tests for well and pump efficiency Power and fuel consumption for pump efficiency

Physicochemical parameters (for changes due to deterioration)

Total and ferric iron, and total manganese (and other metals as indicated) Important anions as identified, including sulfides, sulfates, carbonates, and bicarbonates pH, conductivity, and redox potential (Eh) where possible (instrument readings may be replaced by checking ratios of Fe (total) to Fe2+ (soluble)) Turbidity or total suspended solids calculation of product water Calculation of corrosion/encrustation potential using a consistent method

Microbial

Total Fe/Mn-related bacteria (IRB), sulfur-reducing bacteria (SRB), slime-forming, and other microbial types of maintenance concern as indicated

Visual/physical

Pump and other equipment inspection for deterioration Borehole TV for casing and screen deterioration Electrical parameters: V, A, Ω data, and phase imbalance calculation Listening and feeling change in performance

Source: Modified from Alford et al. (2000).

such as redevelopment, designed to minimize or correct a problem condition. Some actions are considered in Chapter 6.

5.6 A Maintenance Monitoring Protocol for Wells Monitoring is a key part of preventive and proactive maintenance. This section describes decision making, considerations, and recommendations for practical preventive maintenance. Managers of well systems (like those of any engineered system) make operational decisions based on formal or informal cost-benefit analysis. Deciding how to maintain a system properly requires recognizing the risks to the system. Recognition requires knowing what to look for, such as those factors outlined in Chapter 2. Assuming that wells will experience a variety of problems, a variety of risks have to be evaluated, at least initially. It has been established that deteriorating conditions in wells can be complex, and best controlled if detected early. For these reasons, effective maintenance has to be based on regular monitoring, including electro mechanical, physical, chemical, and microbial factors, as well as pump and well service and record keeping. Because of its importance, monitoring is considered here in some detail. Who should do maintenance monitoring? Anyone can be trained to do it, but it requires diligence and attention to detail. As home-well and many other small-facility


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operators neglect such maintenance, perhaps well contractors should provide sevice agreements with well construction contracts, if they do not do so already.

5.6.1 Purposes of Maintenance Monitoring Effective maintenance of wells without monitoring of well parameters is no more possible than effective vehicle maintenance without analysis of engine operation and regular mechanical inspection. Maintenance monitoring of such parameters provides useful knowledge of the nature of problems, which permits reasonable countermeasures to be explored. Repair and replacement intervals and preventive maintenance treatments can then be chosen and fine-tuned accordingly. At a minimum, a preventive maintenance (PM) monitoring program should provide for regular analyses to determine: • Whether a deteriorating condition may be occurring • The reasons for changes in well and pump performance and water quality as soon as they can be detected The effects of chemical action and solids such as silt on well performance, and methods to monitor for them, are typically rather well known to managers of environmental site well arrays. Monitoring for these factors should be relatively easy to sell if there is any commitment to maintenance whatsoever. Biofouling monitoring for wells benefited from the development of rational sampling and suitable analytical methods in the 1990s. Unlike water level, withdrawal rate, and physicochemical and silt and turbidity analyses, biofouling diagnosis methods are still not really standardized (and may never be). For these and other reasons, biofouling monitoring is not as well appreciated. However, biofouling and changes in physical parameters, such as turbidity and sand content, among all the indicators of deteriorating effects, are the most amenable to preventive or early warning monitoring. To be treated effectively, all have to be detected as early as possible. Such monitoring permits making reasonable judgments, for example, of how quickly biofouling is occurring, its effects on the system, and how it can be controlled. (Why Fe, S, and Mn biofouling is a particularly vexing problem for well maintenance is discussed in Chapter 2.) The control of sanding and silting also benefits from early warning so that troubles can be tackled early on, before a pump is ruined or a screen collapses. The recommendations and rationale presented here are designed to be used in presenting a convincing argument to facilities management that well monitoring, including biofouling factors, should be budgeted as a part of a maintenance program designed to protect capital assets and provide the best possible system performance.

5.6.2 Background for Current Monitoring Recommendations The following recommendations are primarily based on the experience of consulting and research projects, including that which culminated in the venerable but now

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out-of-print AWWA Research Foundation publications Methods for Monitoring Iron and Manganese Biofouling in Water Supply Wells (addressing biofouling parameters) that one of us (Smith) completed in 1992 with the valuable assistance of Olli H. Tuovinen and Laura Tuhela-Reuning, then at The Ohio State University, and the more general Evaluation and Restoration of Water Supply Wells, written by Smith, Mary Ann Borch, and Luci Noble for the National Ground Water Association and AWWARF in 1993. We are also indebted to other published reports from colleagues around the world, written or updated in the 1990s. These include good works on performance monitoring. The field with regard to monitoring well deterioration parameters has been largely quiet post-2001 except for polishing, although significant work is being done in related fields such as bioremediation and geothermal energy. There seems to be a new pulse of activity, with the works by Schnieders (2003), Houben and Treskatis (2007), Cullimore (2008), and this one you are reading. A major part of this chapter borrows from (and in the form of its 1995 predecessor, contributes to—this is a feedback loop) Operation and Maintenance of Extraction and Injection Wells at HTRW Sites (EP-1110-1-27), written by Smith, George Alford, and Roy Leach for the U.S. Army Corps of Engineers. This “environmental pamphlet” is a very accessible summary background document (download it from the web) that applies to more situations than the target subject scope. Attempting to maintain systems without such monitoring is virtually pure guesswork, an exercise in gambling on short-term savings without much hope for any payoff in any currency but grief later. This discussion is updated from our year 2000 work. No monitoring program can prevent deteriorating conditions from occurring. However, with such a monitoring program, taking effective countermeasures is possible, resulting in long-term savings. To make use of its monitoring data over time, a maintenance system must have organized and accessible records as described.

5.6.3 Deciding How to Monitor The recommendations of this section should be considered guidance in making decisions about a PM monitoring program rather than a standard guidance of methods or detailed manual of action. Both the monitoring tools available and the methods of employing them have until recently been evolving too rapidly to be formalized into a definite standard procedure. They have, however, now been passing into revisions of standard methods, specifically Standard Methods for the Examination of Water and Wastewater, and some ASTM standard guides. Besides the recommendations here, there are alternative methodologies, essentially variations on a theme, for example, biofouling monitoring methods presented by D. R. Cullimore in Practical Manual of Groundwater Microbiology as part of our publisher’s Sustainable Well Series. If you do not have the second edition, make sure to order one. Selection of a monitoring program should proceed based on a thorough technical assessment of the wells of interest.


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At a minimum (Table 5.2), system operators should monitor:

1. Hydraulic performance, well performance, and pump and motor characteristics (voltage, amperage, vibration, and sound) 2. Physicochemical parameters relevant to the system 3. Indicators of growth or occurrence of biofouling microorganisms in wells

Methods chosen should be as consistent as possible over time, but allow for changes as appropriate. The maintenance monitoring recommendations presented are designed to detect a variety of conditions and symptoms, many of which are interactive. For example, consider a circular interaction situation in which silting is aggravating biofouling clogging, which is reducing the hydraulic efficiency of a well, resulting in initially increased drawdown, which then apparently recovers when the pump subsequently wears and clogs, thereby reducing yield. High motor amperage draw with reduced discharge signifies pump clogging, while low amperage draw and low output indicates a leak somewhere (perhaps indicating corrosion). We will provide some specific monitoring recommendations for the detection and monitoring of deteriorating conditions in wells. Recommendations are made for physicochemical, biological, and hydraulic performance monitoring methods. Selection of a level of monitoring effort should be based on an analysis of the information the methods can provide, as well as the technical needs and financial resources of the facility. The recommendation contains a heavy emphasis on biofouling analysis, since it is among the most troublesome and common problem in wells. Monitoring of hydraulic performance and solids such as sand are equally important in most systems. None of these factors in well deterioration can be profitably neglected. A Note about Cost-Benefit of This Approach: A separate budget analysis serves to determine the long-term cost-benefits of maintenance monitoring and preventive treatment vs. reactive rehabilitation. This should be based upon cost per unit water, and also be factored into LCC calculations (see Chapter 3). Although simple, costper-water calculations provide a useful basis to objectively evaluate cost-benefit for pumping wells. Another system (developed for water supply well systems) is also presented. This spreadsheet-based system can provide rational comparisons among a variety of alternatives, such as monitoring and maintenance (M&M) vs. doing nothing or among different levels of M&M. The cost analyses specific for monitoring well maintenance cannot be defined using a cost-per-unit water basis. The valuation system is a different one entirely. Here you are considering your business goals (Section 3.2). Either you are complying with your consent decree or you are not. Are your clients staying out of court or avoiding “findings and orders”? The cost when the facility is caught in a legal or regulatory web is in the need for repeated sampling events, hours of meetings with lawyers and regulatory people, legal fines and costs, client problems, and community confidence decline and fear. This is the “impairment” of environmental economic value (EEV) discussed in Section 3.3.2.

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5.6.3.1 Incorporating PM Data Collection into the Facility Data Collection Effort Too often the significance and central importance of data are overlooked in the context of the scope of an entire project. What may seem to be minor clerical details to those responsible for a project’s overall management can be important later in facility operations. The quality and completeness of boring logs, well completion diagrams, well testing, etc., are often left to contractors who do not appreciate the value of the data, or left to inexperienced, overworked, or unsupervised junior technical staff. Omissions in the data are often apparent only when it is too late to correct the deficiency. Data are easiest to obtain and more accurate if data collection is incorporated into the project plan at the onset. Compiling data at a later stage of a project’s operation is generally difficult and less successful. Why does this not happen? There is a tendency to omit maintenance planning, data gathering, and repair costs when bids are higher than budgeted, or to inadequately fund these tasks as costs are adjusted to available funds during project management. Budgets to fund remediation activities themselves can be unrealistic in this regard by not adequately considering the real costs of maintenance. Since facility managers and operators are likely to be inexperienced with both the causes of well deterioration and methods for its monitoring and control, seeking outside expert help in getting started is highly recommended. Fortunately, it so happens that there is a community of professionals who are well experienced with these specific methods, their benefits, and limitations. Among these are authors of many of the references cited. Ideally, once properly implemented with adequate training, well maintenance monitoring programs should proceed without outside help unless the facility managers wish to subcontract the M&M.

5.7 Recommended Testing and Information Monitoring Methods The following is a survey of existing monitoring methods and their uses in preventive maintenance and diagnosis of problems.

5.7.1 Visual and Other Sensory Examination Regular visual inspection of the well and pump components is the first line of defense and can reveal important signs of corrosion and encrustation. Problem areas can be observed and a rate of progression ascertained. For better or worse, pumps and pipe components in systems experiencing well deterioration serve as high-cost coupons or sacrificial indicators of corrosion and encrustation, such as those illustrated in Figure 5.2 (also Figures 1.2, 2.3, 2.6–2.8, etc.). Another form of visual inspection is by borehole video camera. Borehole video recording provides direct visual information on the well and can be used to record changes over time. High-resolution color reception is highly useful, and widely available with camera heads of less than 2 in. diameter. The most preferable equipment is that which provides a right-angle color view that permits direct observation of the


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Figure 5.2 (See color insert following page 66.) Some indications that you may have biocorrosion problems in the well (Ohio). Corrosion hole (middle section, top), above pump was losing several 100 gpm.

casing and screen. Figure 5.3 illustrates a typical borehole television system. More important than sophistication in equipment is a knowledgeable camera operator who knows what is likely to be interesting and an observer who can interpret accurately what the camera reveals. Sometimes this is the same person. If not, it helps if the knowledgeable observer is on site when the survey is conducted in order to guide the operator. Familiarity with well components and function is helpful, as the view from inside the well may not be intuitive at first. Although the purchase of a borehole video camera or the hire of its services represents a significant cost, the amount of information that can be obtained in a brief survey makes the survey a good value. Presumptive identification of borehole and casing wall fouling, encrustation, corrosion, and other structural damage can be made rapidly through downhole inspection by the experienced observer. These can be confirmed by direct testing of deposits or equipment retrieved. Sound and other vibratory signals are often crucial early indicators of problems. If the well sounds different when it is pumping, the pump or piping vibrates, valves shutting or opening sound different, there is a sizzling or crackling, or a bubbling, these are signs that some change has happened in the well.

5.7.2 Well and Pump Performance Well and pump performance changes are inevitable and occur as a function of time as a result of many processes. But to many operators or those responsible for wells, it appears that somewhat mysteriously the well just ceases to perform as needed, leaving everyone in a crisis. Worse yet, when the well ceases to function, it is not known whether it is a problem with the well, the pump, or both. However, one can monitor and track changes in well and pump performance, thus planning for and performing needed maintenance and avoiding a crisis. To do so, facilities need to establish a well

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Figure 5.3 Down- and side-view borehole video camera system operated by Geoscope Inc., Mansfield, Ohio.

and pump performance monitoring program to systematically collect data, analyze it, discern trends, and take action. Two priorities stand out in establishing a well and pump performance monitoring program: (1) benchmark the original performance, and (2) be sure to compare “apples with apples,” not “apples with oranges.” Common to both priorities is the need for consistency, which is maintained through set procedures for collecting and analyzing the data. This implies a need to train the responsible personnel in the set procedures and for someone to understand what the results of the analysis are telling them. 5.7.2.1 Benchmarking We benchmark the performance of both the well and the pump as a standard with which to compare and to discern trends in the future. It is preferable that the baseline performance be performance when new. In the case of the typical centrifugal well pump, establishing the baseline performance of the pump is relatively easy. This is provided by the pump manufacturer as a pump performance curve (Figure 5.4 is an example). The pump performance curve plots the relationship of the output from the pump (discharge rate, e.g., gal/min, gpm)


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Figure 5.4 Example pump performance curve (Scherer, 1993, AE-1057, North Dakota State University Extension). Note: HP and head are per stage.

as it pumps against a given total dynamic head (e.g., feet of water or lb/in.2, PSI). Ideally, using this information, the pump is sized for the specific conditions of the well, system, and intended pumping rate. Plotting the point of intended pumping rate vs. total dynamic head permits designing a system in which performance would fall on the performance curve in the range of maximum efficiency of the pump. Manufacturers of pump motors will provide information on the current requirements (amps) that the new motor will draw in an appropriate application. This current requirement is an indicator of the baseline performance of the pump motor. Establishing the baseline performance of the well can be accomplished with a step-drawdown test (well described by publications in our reading list). This method consists of pumping the well at steps of increasing discharge rates, with each step continuing until the pumping water level begins to stabilize (Figure 5.5). Throughout each step, water levels are regularly measured and recorded, and the discharge rate is accurately monitored and maintained. When the step-drawdown test data are analyzed (Figure 5.6), we can separate out the aquifer drawdown and well loss drawdown components of the total drawdown observed in the well during pumping (Figures 5.6 and 5.7). The function for aquifer and well loss parameters and total well drawdown in a screened sand and gravel well may be represented:

Total drawdown (ft or m) = BQ + CQ2

(5.1)

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Sustainable Wells: Maintenance, Problem Prevention, and Rehabilitation Village Well No. 5 Step-Drawdown Test Time-Drawdown Data

0 10

159 g.p.m 203 g.p.m

20 Drawdown (ft.)

30

298 g.p.m

40 50

401 g.p.m

60 70

464 g.p.m

80 90 100

0

20

40

60

80

100

120

140

160

180

200

Time (min.)

Figure 5.5 A plot of step-drawdown test data.

Village Well No. 5 Step Test Analysis

0.20 0.19 0.18 1/Specific Capacity

0.17 0.16 0.15 0.14

C = 1.71E-04

0.13 0.12 0.11 B = 0.082

0.10 0.09 0.08

0

50

100

150

200 250 300 Pumping Rate (g.p.m.)

350

400

450

500

Figure 5.6 Analysis of step-drawdown test using Hantush-Bierschenk straight-line method, B established by intercept and C from slope of plot.

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Aquifer Loss & Total Drawdown (ft.)

Village Well No. 5 Aquifer Loss & Total Drawdown 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160

Aquifer loss

Well loss Total drawdown

0

100

200 300 Pumping Rate (g.p.m.)

400

500

Figure 5.7 Graph of efficiency vs. pumping rate from analysis of step test plot, aquifer loss, and well loss illustrated.

where B = aquifer loss parameter, C = well loss parameter, and Q = pumping rate (gpm). The exponent in CQ2 may vary slightly from "2." Note: American engineering units (gpm and feet) or SI engineering units (L/s, m) (rather than consistent units) may be used in the analysis. The BQ factor represents the water level drawdown (that is, energy) required to move water through the aquifer toward the well when pumping. The CQ2 factor represents the water level drawdown (energy) to move water from the aquifer through the gravel pack and screen into the well. Several parameters of well performance can be derived from the step-drawdown test. First, we can establish a specific capacity of the well. This is a single value relationship of a given output (discharge rate, Q, e.g., gpm) at a given water level change (usually feet or meters of drawdown, s) expressed in the units of

Specific capacity (Q/s) = gpm/ft of drawdown

Specific capacity (Q/s) is only useful for comparison purposes if the value is derived from a consistent pumping rate. We generally state Q/s as

x gpm/ft of drawdown at y gpm

Second, we can establish the efficiency of the well. This is the ratio of the water level drawdown in the aquifer to the total water level drawdown in the well at a given pumping rate, expressed as a percent:

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Sustainable Wells: Maintenance, Problem Prevention, and Rehabilitation Village Well No. 5 Estimated Efficiency

100 90

% Efficiency

80 70 60 50 40

0

100

200

300 400 Pumping Rate (g.p.m.)

500

600

700

Figure 5.8 Plot of percent well efficiency vs. pumping rate. Derived from analysis illustrated in Figures 5.5 and 5.6, with extrapolations to gpm above and below the tested flow rates (Figure 5.5).

% Efficiency = (BQ/(BQ + CQ2))*100

(5.2)

Again, efficiency is only useful for comparison purposes if the value is derived from a consistent pumping rate. We generally state efficiency as

x% efficiency at y gpm

Third, we can use the results of the step-drawdown test and the functions presented above to produce useful curves documenting the performance of our individual well over a wide range of pumping rates. For example, we can plot the total drawdown (ft) vs. puming rate (gpm). Or we can plot percent efficiency vs. pumping rate (Figure 5.8). 5.7.2.2 Compare Apples with Apples Now that we have documented the baseline performance of our pump and well when new, we can track the performance changes over time with a performance monitoring program. We need to regularly obtain the same raw data and perform the same interpretations as the benchmarking process. Therefore, we need regular measurements of: • Total dynamic head (TDH) (e.g., ft H2O, or PSI), the pump is working against • Pumping rate (Q) (e.g., gpm) • Current draw on each leg of the pump motor (amps) • Water level measurements, both static and pumping (e.g., ft)

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From these data we will be able to derive the same performance parameters that were benchmarked. This is where consistency is an issue. For example, when water levels are measured, they should always be measured from the same reference point, called the measuring point. If each employee who collects a water level measurement does so from a different reference point, the data collected will be of little use. This is why explicit procedures and training are important. Ideally, the wellhead should be equipped to facilitate consistent manual measurements of these parameters or a SCADA (supervisory, control, and data acquisition) system installed to automatically monitor them (more on that below). The data and interpretations need to be entered into some sort of record system (more on that below). 5.7.2.3 Monitoring Pump and Pump Motor Performance Somewhere at the wellhead, a pressure gauge needs to be installed in the discharge line ahead of any valves used to regulate the discharge from the pump. From this gauge we obtain the head the pump is pumping against at the elevation of the gauge. We also measure a pumping water level, which needs either to be measured directly with the gauge as the reference point, or the depth to water corrected to indicate depth below the pressure gauge. For our purposes, the total dynamic head (TDH) will be the sum of the two:

TDH (e.g., ft H 2O) = depth to pumping water level (ft) + gauge reading (ft H 2O)

(5.3)

Additional accuracy can be obtained by including velocity losses up the riser pipe, friction losses in the riser pipe accounting for pipe roughness (if significant), losses from pipe bends, etc. Your consulting engineer should be able to help provide values for these other losses. Also at the wellhead, we need an accurate measurement of the pumping rate. Flow meters of various designs are available for this. Now we can go back to the pump performance curve provided by the manufacturer (Figure 5.4 is an example) and compare the head generated by the pump (ft H 2O) against the pumping rate (gpm). If the point falls on the original performance curve, then the pump is performing as designed. If the point falls below the curve, then the pump is beginning to wear. As the pump’s performance begins to decline, the point moves away from the range of maximum efficiency, thus consuming more energy for the water pumped. Also check the current draw for each leg against the manufacturer’s data. If the current draw is increasing, it is an indicator of developing problems in either the pump or motor. A complete guide to troubleshooting pump and motor problems is beyond the scope of this work. The reader is referred to Butts (2006) and the Water Systems Council (2002) for more detailed information on this subject (see our recommended reading list). 5.7.2.4 Tracking Well Performance Utilizing the water level that has been measured, calculate the current water level drawdown (s). Use the drawdown value and current pumping rate (Q) data that have been collected (as described above) to calculate a current specific capacity (Q/s) for

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the well. Compare this to the benchmark specific capacity (assuming that both values were calculated at a consistent pumping rate). If the pumping rate is not a constant, then the values for drawdown and pumping rate can be compared to the benchmark curve prepared when the well was new. Well hydraulic performance monitoring should consist of regular (e.g., monthly or quarterly) measurements of pump operation and well hydraulic characteristics, as follows:

1. Pumping dynamic water level (DWL) (pumping water level, PWL) in pumping wells 2. Static DWL (“true” static water level (SWL) or static DWL at the well with the pump off but under the influence of nearby pumping wells) for all wells 3. Area water levels to keep track of seasonal, tidal, or other effects that may affect well DWL 4. Wellhead pumping rate and operating hours for regularly pumping wells 5. For regularly pumping wells, pump power consumption and power characteristics (voltage, amperage draw, occurrence of stray currents), especially noting how each varies from the manufacturer’s nominal specifications

The pumping rate should be determined against a consistent system head (if pumping into a collection system) and periodically against free discharge if feasible. Methods of hydraulic pump testing and motor characteristics tests are widely known and referenced (see our reading list). The Water Systems Handbook (Water Systems Council) and some motor references provide very useful troubleshooting (diagnostic) charts. For environmental monitoring wells, slug tests (see the reading list) also can be used to detect changes in hydraulic conductivity for low-production monitoring wells as long as there is a historical record. Their utility in well maintenance and rehabilitation is less direct than with step-drawdown tests, but data derived from these tests can be used in preliminary calculations of expected well hydraulic parameters. As with constant rate pumping test data, calculations of aquifer characteristics based on slug test data can be used for estimation of theoretical well mounding in injection wells. If changes in conductivity are noted and there are no other hydrologic reasons, fouling of the well may be occurring. Because of the small volumes of water involved and the short (or long) time span over which the test occurs, pressure transducers and digital data logging are generally employed. Pressure transducers are submerged in the well and register the pressure of the column of water overlying them. Water level changes are detected as changes in pressure as the height of the overlying water column either increases or decreases. The data logger can be programmed to sample and record data from the transducer at required time intervals. This feature of digital data logging is most useful when conducting slug tests in high-permeability sediments where many water level measurements will be required over a span of seconds as the water level rapidly recovers.


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In general, for arrays of monitoring and pumping wells, such as those used for plume control, automatic sensor-recorder methods make excellent sense in providing a lot of information with minimal operator labor or contact with contaminated fluids (if present). Special Conditions: Hazardous cleanup sites may impose restrictions on optimal step testing methodology. For example, a five-step test with pressure measurement is recommended to determine pump wear (as distinguished from well performance parameters). However, pumping contaminated ground water requires collection of the fluid. Perfecting the gathering of pump wear data from a three-step test, and learning to extrapolate from short steps, may be a necessary compromise in methodology. Site managers of environmental projects typically have access to database systems with graphical output. Drawdown data from water level monitor output files can be input to the program for the well array, and anomalies such as increased drawdown at particular wells can be displayed. 5.7.2.5 Water Level Measurement Recommendations • Water level data may be collected manually or the process automated. • For relatively small numbers of wells and conditions where personnel are not at health risk when water columns are exposed: Use electric water level probe and manual data entry. • For larger numbers of wells where personnel time would be inordinately devoted to water level measurements: Use automated water level recording via transducers. • For conditions where exposure to vapors off-gassing from well fluids poses an inhalation hazard: Use automated water level recording via transducers. Several approaches to water level measurement are possible, each with its advantages and disadvantages. Table 5.3 summarizes water level measurement methods and their features. Note: Airlines are a traditional method of water level measurement. However, they are very inaccurate and prone to clogging. We do not recommend their use. Note that all conventional water level measurement systems are fouled by nonaqueous-phase liquids and will yield inaccurate results. There are specialized instruments for dual-phase level detection. 5.7.2.6 Well Discharge Measurement Each pumping well and receiving well or discharge should be metered. Total system pumping production should match total discharge. Unbalances may indicate leaks or metering inaccuracies.

1. Flow meters should be sized to the expected well discharge rate. Instantaneous and totalized flow readings in commonly used volume-rate units (m3/h, gal/min, etc.) are necessary.

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Table 5.3 Features of Water Level Measurement Methods Type of Water Level Measurement

Advantages

Disadvantages

Electric sounder

Commonly available; reliable when maintained; accurate under most water-only conditions (±0.02 in.); not highly subject to downhole fouling; one sounder can be used on multiple wells

Requires wellhead access and unobstructed water surface access; probe will foul in floating material on water surface; mechanical aging of conductor wire must be considered; cross-contamination is possible; requires personnel to take levels and manually enter data

Airline (gauge measurement) or instrument measurement)

Inexpensive; no need for direct access to water level surface; each well has a dedicated airline

Relatively inaccurate (+1 in. or more); subject to fouling; requires personnel for taking levels and manual entry of data

Airline (instrument measurement)

Inexpensive; no need for direct access to water level surface; each well has a dedicated airline; with instrument, improves accuracy to electric water level sounder range; data recording possible

Subject to fouling; requires personnel for taking levels

Water level transducers

Relatively accurate when properly selected and maintained; permit automatic data querying in SCADAa system; dedicated to well; no personnel exposure to water; no direct water access needed

Relatively expensive per unit; requires regular maintenance to deter fouling; if maintenance not performed, automatic systems may record inaccurate (useless) data

Source: Modified from Alford et al. (2000). Supervisory, control, and data acquisition. Note that all these water level monitoring methods provide data that can be manually entered into SCADA databases.

a

2. Flow measurement method selections should take into consideration the quality of the fluid to be measured. Clogging fluids may foul turbine flow meters. Acoustic devices may have better service lives under some circumstances. Systems standard to industrial waste water treatment applications should suffice. 3. At a minimum, measurements should be taken manually daily to weekly, depending upon fluctuation. 4. Wherever possible, flow meters should have automatic readouts, either to a central SCADA system or readout device. Systems standard to industrial water supply should suffice.


141

5.7.2.7 Pressure Measurement Either manually read or digital read-out meters may be used. With both, plugging of sensor orifices is to be expected. To detect pressure changes in the conveyance system, pressure should be measured as near as possible to the wellhead (immediately downstream of the pump discharge check valve. Measurements should be taken daily to weekly. Automation facilitates data collection. 5.7.2.8 Electrical (Power) Changes in pump motor amperage (A) draw and circuit voltage (V) and ohms (Ω) are used to detect problems on the power side.

1. V should be within ±10% of the motor nameplate voltage (or within stated manufacturer’s specification) when the motor is under load (running). Larger V variations may cause winding damage. These should be corrected in the power supply or the motor changed to match the supplied V characteristics if it remains constantly high or low. 2. Increases in amperage on start or run cycles over listed service factor amps indicate: • Loose terminals in the control box or possible cable defect • Too high or low service V • Motor windings are shorted • Mechanical resistance such as sand in bearings 3. A drop in typical “run” amperage indicates a loss of mechanical resistance against motor operation. This datum, in combination with reduced pump discharge rate or pressure data, can be used to confirm that a problem has developed in pump output, such as the development of a hole in the pump discharge pipe. 4. Deviations in circuit ohms indicate wiring problems. A low value on one or more line legs indicates a potential motor short. Greater than normal values indicate poor cable connections or joints or that windings or cables may be open. If some values are higher than normal and others lower than normal, drop leads may be mixed. 5. Megaohm (MΩ) detections outside the circuit indicate ground faults. For a motor installed in a well: If resistance between any wire lead and true ground is

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