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Preface to Second Edition x
Preface to First Edition xi
Lewis Clark (1937-2004): An Appreciation xiii
Acknowledgements xiv
1 Introduction 1
1.1 Wells and boreholes 1
1.2 Groundwater occurrence 5
1.2.1 Aquifers, aquicludes and aquitards 5
1.2.2 Porosity and aquifer storage 12
1.3 Groundwater flow 17
1.3.1 Darcy's equation 17
1.3.2 General equations of groundwater flow 21
1.3.3 Radial flow to wells 25
2 Groundwater Investigations for Locating Well Sites 28
2.1 Desk studies 31
2.2 Field reconnaissance 35
2.3 Well survey 36
2.4 Geophysical surveys 41
2.4.1 Electrical resistivity 42
2.4.2 Electromagnetics 49
2.5 Drilling investigations 52
2.6 Groundwater resources assessment 59
2.6.1 Inflow estimation: direct recharge 61
2.6.2 Inflow estimation: indirect recharge 64
2.6.3 Aquifer response analysis 65
2.6.4 Outflow estimation 66
2.6.5 Catchment water balance and modelling 66
2.7 Groundwater quality 69
2.7.1 Introduction 69
2.7.2 Chemical composition of groundwater 69
2.7.3 Groundwater for potable supply 72
2.7.4 Groundwater for irrigation 77
2.8 Pollution risk assessment and prevention 78
2.8.1 Groundwater vulnerability 79
2.8.2 Wellhead protection areas 81
2.8.3 Estimating the pollution risk for a new well site 85
2.9 Planning the well scheme 87
3 An Introduction to Well and Borehole Design 91
3.1 Drilled wells 91
3.1.1 General design principles 91
3.1.2 Wells in crystalline aquifers 96
3.1.3 Wells in consolidated aquifers 100
3.1.4 Wells in unconsolidated aquifers 104
3.1.5 Economic considerations in well design 107
3.2 Hand-dug wells 109
3.2.1 Design for yield 113
3.2.2 Design for health 114
3.3 Infiltration galleries 116
3.4 Radial collector wells 120
3.5 Observation boreholes 120
3.6 Exploration boreholes 125
3.7 Pump selection 125
3.7.1 Vertical turbine pumps 128
3.7.2 Electrical submersible pumps 129
3.7.3 Motorized suction pumps 133
3.7.4 Helical rotor pumps 134
3.7.5 Hand pumps 135
4 Issues in Well Design and Specialist Applications 140
4.1 Choice of construction materials 140
4.1.1 Strength 141
4.1.2 Jointing system 141
4.1.3 Durability 143
4.1.4 Chemical inertness 143
4.1.5 Standards 144
4.2 Casing 145
4.2.1 Steel casing 145
4.2.2 Plastic and fibreglass casing 146
4.3 Screen 147
4.3.1 Slot design and open area 147
4.3.2 Slot width 149
4.4 Gravel pack design 150
4.4.1 Natural gravel pack 150
4.4.2 Artificial gravel pack 151
4.5 Hydraulic design 154
4.5.1 Partial penetration effects 156
4.5.2 The damage zone and well bore skin 158
4.5.3 Gravel pack loss 159
4.5.4 Screen entrance loss 159
4.5.5 Well upflow losses 162
4.6 Economic optimization of well design 167
4.6.1 General principles 167
4.6.2 Example 168
4.7 Groundwater and wells for heating and cooling 171
4.7.1 Groundwater for cooling 172
4.7.2 Heating with groundwater: geothermal fluids 173
4.7.3 Heating with groundwater: heat pumps 174
4.7.4 Well configurations 175
4.8 Well doublets 177
4.8.1 Hydraulic equations 178
4.8.2 Feedback and breakthrough 178
4.8.3 Water chemistry 179
4.9 Recharge wells 180
4.9.1 Purpose 180
4.9.2 Construction of injection wells 182
4.9.3 Installations 183
4.9.4 Testing and operation 184
4.9.5 Clogging of recharge wells 184
4.9.6 Seismic risk from water injection 188
4.10 Aquifer storage and recovery 188
5 Well and Borehole Construction 191
5.1 Percussion (cable-tool) drilling 193
5.1.1 Drilling in hard-rock formations 196
5.1.2 Drilling in soft, unstable formations 198
5.1.3 Light-percussion drilling 201
5.2 Rotary drilling 202
5.2.1 Direct circulation rotary 202
5.2.2 Fluids used in direct circulation rotary drilling 208
5.2.3 Reverse circulation 212
5.2.4 Top-hole and down-the-hole hammer drilling 215
5.2.5 Dual rotary 217
5.2.6 Borehole testing during drilling 218
5.2.7 Methods of casing and screen installation 220
5.3 Sonic drilling 221
5.4 Auger drilling 222
5.5 Jetting 223
5.6 Direct push and drive sampling 224
5.7 Driving of well-points 226
5.8 Manual construction 226
5.9 Well development 228
5.9.1 Well and aquifer damage 229
5.9.2 Developing the well 229
5.9.3 Developing the aquifer around the well 229
5.9.4 Methods of development 231
5.9.5 Disinfecting the well 240
5.10 Wellhead completion 240
6 Formation Sampling and Identification 244
6.1 Observing the drilling process 244
6.1.1 Observing the drilling process in hard-rock aquifers 247
6.2 Collecting formation samples 248
6.2.1 Disturbed formation sampling 248
6.2.2 Undisturbed formation sampling 256
6.3 Description and analysis of drilling samples 260
6.3.1 Characterizing disturbed samples 261
6.3.2 Characterization of representative samples 261
6.3.3 Characterization of undisturbed samples 267
6.4 Downhole geophysical logging 269
6.4.1 The geophysical logging package 270
6.4.2 Organizing a geophysical logging mission 275
6.4.3 On arriving on site 275
6.4.4 Formation logs 276
6.4.5 Fluid logs 283
6.4.6 Well construction logs 287
6.5 Downhole geophysical imaging 287
6.6 Distributed (fibre-optic) temperature sensing (DTS) 290
6.7 Preparing a composite well log 292
7 Well and Borehole Testing 295
7.1 Objectives of test pumping 295
7.1.1 Well performance 295
7.1.2 Water quality 296
7.1.3 Sustainability 296
7.1.4 Environmental impacts 298
7.1.5 Aquifer properties 298
7.2 Planning a well pumping test 298
7.2.1 Before starting 298
7.2.2 When to test pump 301
7.2.3 Consents and permissions 301
7.2.4 Equipment 302
7.2.5 The observation network 308
7.2.6 Recording of data 313
7.3 Types of pumping test 315
7.3.1 Dimension pumping 315
7.3.2 The step test 315
7.3.3 Medium to long-term (constant rate) test 316
7.3.4 Recovery test 317
7.4 Analysis of test pumping data from single wells 317
7.4.1 Fundamentals 317
7.4.2 The misuse of test pumping analysis 318
7.4.3 Well performance - the step test 320
7.4.4 Steady-state analyses 323
7.4.5 Time-variant analysis 326
7.4.6 Analysis of recovery tests 331
7.5 Multiple wells 334
7.5.1 Steady-state analysis of multiple pumping wells 334
7.5.2 Time-variant analysis of multiple wells 334
7.5.3 Application of the Cooper- Jacob approximation to multiple wells 334
7.6 The shape of the yield-drawdown curve: Deviations from the ideal response 335
7.6.1 A non-infinite aquifer: Presence of an impermeable barrier 336
7.6.2 Recharge during a pumping test 336
7.6.3 Unconfined aquifers: Delayed yield 339
7.6.4 Poroelasticity, subsidence and the 'Noordbergum Effect' 341
7.6.5 Large diameter wells 341
7.6.6 Diagnostic plots 342
7.7 Interpretation of pumping and recovery test data in hard-rock aquifers 344
7.7.1 High yielding hard-rock wells 345
7.7.2 Low-yielding hard-rock wells 346
7.7.3 Sustainable yield of hardrock wells 348
7.8 Single borehole tests: slug tests 350
7.8.1 Slug tests 350
7.8.2 Packer testing 352
7.9 Tracer tests 353
7.10 Geophysical logging during pumping tests 355
7.11 Test pumping a major well field: the Gatehampton case study 356
7.12 Record-keeping 359
8 Groundwater Sampling and Analysis 361
8.1 Water quality parameters and sampling objectives 363
8.1.1 Master variables 363
8.1.2 Main physicochemical parameters 363
8.1.3 Major ions 364
8.1.4 Drinking water 365
8.1.5 Water for agricultural and industrial purposes 367
8.1.6 Pollution-related parameters 367
8.1.7 Indicator parameters 369
8.1.8 Microbiological quality and indicator parameters 370
8.2 Field determinations 373
8.2.1 The purpose of field determinations 373
8.2.2 Downhole sondes and throughflow cells 374
8.2.3 Field kits for other parameters 375
8.2.4 Emergency water supply 377
8.3 Collecting water samples from production wells 380
8.3.1 The sample line 380
8.3.2 When to sample: well testing 380
8.3.3 When to sample: production wells 382
8.4 Collecting water samples from observation boreholes 383
8.4.1 Preparation for sampling 383
8.4.2 Bailers and depth samplers 384
8.4.3 Simple pumps 386
8.4.4 Submersible pumps 386
8.4.5 Other pumps 387
8.4.6 Sampling at specific depths 389
8.4.7 Sampling for non-aqueous phase liquids 391
8.5 Sample filtration, preservation and packaging 392
8.5.1 Sampling order 394
8.5.2 Physicochemical parameters 394
8.5.3 Microbial parameters 396
8.5.4 Inorganic parameters: acidification and filtration 397
8.5.5 Inorganic parameters: sampling 400
8.5.6 Organic parameters 400
8.5.7 Stable isotopes 403
8.5.8 Dissolved gases 404
8.6 Packing and labelling samples 406
8.7 Quality control and record keeping 407
8.8 Sample chemical analysis 408
8.9 Hydrochemical databases 412
9 Well Monitoring and Maintenance 414
9.1 Factors affecting well system performance 415
9.1.1 Physical processes 415
9.1.2 Chemical processes 416
9.1.3 Microbiological processes 421
9.1.4 Well design and construction 423
9.1.5 Well system operation 423
9.2 Monitoring well system performance 424
9.2.1 Monitoring well performance 425
9.2.2 Well inspection tools 433
9.2.3 Pump performance 434
9.2.4 Water quality monitoring 436
9.2.5 Monitoring microbial processes 436
9.3 Well maintenance and rehabilitation measures 437
9.4 Well decommissioning 443
10 Well and Borehole Records 446
10.1 Well archives 446
10.2 Operational well databases 447
10.3 An example of a hydrogeological database - Afghanistan 454
Appendix 1 Units and Conversion Tables 458
Appendix 2 Hydraulic Equations for
Groundwater Engineers 460
Appendix 3 Health and Safety Plans 464
Appendix 4 World Health Organization
Drinking Water Guidelines 467
Appendix 5 FAO Irrigation Water
Quality Guidelines 473
References 475
Index 506
Water wells in some form or other have existed for almost as long a time as people have occupied this planet. The earliest wells were probably simple constructions around springs and seeps, or shallow excavations in dry river beds, but such wells have not left any traces for archaeologists. One of the oldest well discoveries is in Cyprus, dating from 7000 to 9000 BC (Fagan, 2011), whilst the earliest well remains in China have been dated at around 3700 BC (Zhou et al., 2011). Since the first millennium BC, horizontal wells or qanats have been widely used for water supply and irrigation in the Middle East and western Asia, notably Iran, and continue to be used today (Figure 1.1). In Europe, the development of many towns and cities in the middle ages and on through the industrial period was aided considerably by the abstraction of relatively pure water supplies from wells and springs (Figure 1.2). In the nineteenth century, new drilling technology was used to construct deep wells to exploit artesian (flowing) aquifers (see Section 1.2 for explanations of aquifer terminology), including the Grenelle well in the Paris basin, which was drilled between 1833 and 1841, and reached a depth of 548?m (Margat et al., 2013). The first mechanically-drilled well in the United States dates from 1823, whereas the first drilled well in the Great Artesian Basin of Australia was constructed in 1878 (Margat and van der Gun, 2013).
Figure 1.1 Open section of falaj (qanat) running through a town in northern Oman. Here, the channel is divided into three, with two of the channels then rejoining (at the bottom of the picture), in order to produce a two-thirds: one third split in the flow downstream. This Falaj al Khatmeen is included on the UNESCO list of World Heritage Sites.
Photo by Bruce Misstear
Figure 1.2 Hand-dug well in Brittany, France.
Wells continue to have an important role in society today. Some 2 billion people obtain their drinking water supplies directly from drilled or hand-dug wells (UNICEF and WHO, 2012). A further 4 billion people have access to piped water or public taps, a proportion of which will be sourced from groundwater, so it is likely that more than 3 billion people worldwide rely on water wells for their drinking water. Over half the public water supplies in European Union countries come from groundwater, ranging from between 20% and 30% of drinking water supplied in Spain and the United Kingdom, to nearly 100% in Austria, Lithuania and Denmark (Hiscock et al., 2002).
The largest use of groundwater worldwide is for irrigation (70%), with India, China and the United States the leading countries in terms of total groundwater withdrawals (Margat and van der Gun, 2013). The last 30 years have witnessed a huge increase in the use of wells for agricultural irrigation, especially in Asia (Figure 1.3): in China 54% of irrigation water is supplied from groundwater while this proportion rises to 89% in India and 94% in Pakistan. In the United States, groundwater pumping increased by 144% between 1950 and 1980, with 71% of the annual withdrawal of 111.7?km3 in 2010 being used for irrigated agriculture (Margat and van der Gun, 2013). According to the National Ground Water Association, 44% of the population of the United States depends on groundwater for its drinking water and there are about 500?000 new private wells constructed each year for domestic supplies.
Figure 1.3 A dual purpose irrigation and drainage well in the Indus valley, Pakistan. In this 'scavenger well' the outlet pipe in the foreground of the picture is discharging fresh groundwater from the upper part of the well, whereas the pipe to the right is discharging saline water from the lower section of the well, thus preventing the saline water from moving upwards and contaminating the good quality water. The good quality water is used for irrigation whilst the saline water is diverted to the drainage system.
Other uses of wells are many and diverse and include livestock watering (Figure 1.4), industrial supplies, geothermal energy or ground-source heating/cooling (Figure 1.5), construction dewatering, brine mining, water injection to oil reservoirs, aquifer clean up, river support and artificial recharge of aquifers. Wells and boreholes are also used extensively for monitoring water levels and groundwater quality.
Figure 1.4 Drilled well fitted with a windmill pump used for livestock watering, New South Wales, Australia.
Figure 1.5 Drilling rig being set up for constructing a well in a gravel aquifer used as a source of geothermal energy, Dublin, Ireland.
Wells have long had a religious significance in many societies. In India, the Holy Vedic Scriptures dating back to 8000 BC contain references to wells (Limaye, 2013). In the Bible and Koran, wells and springs feature prominently, sometimes as places for meeting and talking and often as metaphors for paradise. Holy wells remain an important feature of local culture throughout the Celtic lands in western Europe, for example, where there may be as many as 3000 holy wells in Ireland alone (Logan, 1980; Robins and Misstear, 2000). Many of these wells are still visited regularly and votive offerings such as rags, statues and coins are common (see Box 3.7 in Chapter 3).
Water wells have also been a source of conflict since Biblical times:
But when Isaac's servants dug in the valley and found there a well of springing water, the herdsmen of Gerar quarrelled with Isaac's herdsmen, saying "This water is ours".
Genesis 26:19-20
They remain so today. A major point of contention in the Middle East is the control of the groundwater resources in the region (Shuval and Dweik, 2007; Younger, 2012).
Water wells come in many forms, orientations and sizes. Traditionally most water wells were excavated by hand as shallow, large diameter, shafts; nowadays, the majority are constructed from relatively small diameter boreholes drilled by machine, sometimes to great depths. Water wells are typically vertical but can be horizontal (infiltration gallery), a combination of vertical and horizontal well (radial collector well), or occasionally inclined (Figure 1.6). The water may be abstracted by hand-operated or motorized pumps, or it may flow to the surface naturally under positive upward pressure (artesian well; Figure 1.7) or by gravity drainage (qanat or falaj). This book deals mainly with drilled wells (often called boreholes), since readers are likely to encounter these most often, but other types of wells are also covered.
Figure 1.6 Examples of different types of water well
Figure 1.7 Flowing artesian well, northern Myanmar. The well was drilled into a strongly confined sandstone aquifer. Children are enjoying the 'swimming pool' created by the discharge until such time as the well is capped.
Water well terminology is not standard throughout the world, and different names are commonly applied to identical constructions. The terms used in this book are explained in Box 1.1. Further details of the different types of wells and boreholes, and their component parts, are included in Chapter 3.
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