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- Herausgeber: John Wiley & Sons
- Kategorie: Wissenschaft und neue Technologien
- Serie: The Geological Field Guide Series
- Sprache: Englisch
The fourth edition of this bestselling textbook has been fully revised in order to present the most up-to-date and comprehensive guide to completing a hydrogeological study. Beautifully presented with full colour photos and diagrams throughout, Field Hydrogeology retains its practical pocket size for easy use in the field. This new edition includes all the recent developments in the environmental regulations, with particular focus on the use of innovative technology. New topics include geothermal energy, soakaways, marrying manual water level readings with logger records, prediction of long-term drawdown and lateral extent of impacts, and flow measurement in locations with small head gradients.
With case studies and text boxes to aid comprehension, and a particular emphasis on practical application, this is an essential tool for students taking Hydrogeology and/or field course modules in Geology, Earth Sciences, Hydrogeology and Engineering courses.
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Veröffentlichungsjahr: 2017
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Table of Contents
Cover
The Geological Field Guide Series
Title Page
Copyright
Dedication
PREFACE
ACKNOWLEDGEMENTS
Chapter 1: INTRODUCTION
1.1 Groundwater Systems
1.2 Conceptual Model
1.3 Groundwater Computer Modelling
1.4 Hydrogeological Report Writing
1.5 Expert Witness
Chapter 2: DESK STUDY
2.1 Defining the Area
2.2 Identifying the Aquifers
2.3 Groundwater Levels
2.4 Surface Water
2.5 Recharge
2.6 Groundwater Use
2.7 Groundwater Chemistry
2.8 Aerial Photographs and Satellite Imagery
2.9 Planning a Fieldwork Programme
Chapter 3: FIELD EVALUATION OF AQUIFERS
3.1 Grain Size Analysis
3.2 Hydraulic Properties of Aquifers
3.3 Hydraulic Properties and Rock Types
3.4 Assessing Hydraulic Properties
3.5 Using Hydraulic Property Information
Chapter 4: GROUNDWATER LEVELS
4.1 Water-Level Dippers
4.2 Continuous Water-Level Recorders
4.3 Measuring Ground Levels and Locations
4.4 Tool-Box
4.5 Well Catalogue
4.6 Field Surveys for Wells, Boreholes and Springs
4.7 Interpretation of Abstraction Borehole Water Levels
4.8 Groundwater-Level Monitoring Networks
4.9 Groundwater-Level Fluctuations
4.10 Managing Groundwater-Level Data
4.11 Constructing Groundwater Contour Maps and Flow Nets
4.12 Interpretation of Contour Maps and Flow Nets
4.13 Using Other Groundwater Information
Chapter 5: RAINFALL, SPRINGS AND STREAMS
5.1 Precipitation
5.2 Evaporation
5.3 Springs
5.4 Stream-Flow Measurement
5.5 Stage–Discharge Relationships
5.6 Choosing the Best Method
5.7 Processing Flow Data
Chapter 6: PUMPING TESTS
6.1 What Is a Pumping Test?
6.2 Planning a Pumping Test
6.3 Pumps and Pumping
6.4 On-Site Measurements
6.5 Pre-Test Monitoring
6.6 Test Set-up
6.7 Step Tests
6.8 Constant Rate Tests
6.9 Recovery Tests
6.10 Pumping Test Analysis
6.11 Tests on Single Boreholes
6.12 Packer Tests
Chapter 7: GROUNDWATER CHEMISTRY
7.1 Analytical Suites and Determinands
7.2 Sampling Equipment
7.3 Sampling Protocols
7.4 Monitoring Networks
7.5 Using Chemical Data
Chapter 8: RECHARGE ESTIMATION
8.1 Water Balance
8.2 Rainfall Recharge
8.3 Induced Recharge
8.4 Other Sources of Recharge
Chapter 9: SPECIALIST TECHNIQUES
9.1 Borehole and Piezometer Installation
9.2 Down-Hole Geophysics
9.3 Using Artificial Tracers
Chapter 10: PRACTICAL APPLICATIONS
10.1 Borehole Prognoses
10.2 Groundwater Supplies
10.3 Wells in Shallow Aquifers
10.4 Contaminated Land Investigations
10.5 Landfills and Leachate
10.6 Geothermal Energy
10.7 Groundwater Lowering by Excavation
10.8 Rising Water Tables
10.9 Soakaways
10.10 Investigating Wetland Hydrology
Appendix A: GOOD WORKING PRACTICE
A1.1 Safety Codes
A1.2 Safety Clothing and Equipment
A1.3 Distress Signals
A1.4 Exposure or Hypothermia
A1.5 Heat Exhaustion
A1.6 Working Near Wells, Boreholes and Monitoring Piezometers
A1.7 Hygiene Precautions for Water Supplies
A1.8 Trial Pits
A1.9 Electrical Equipment
A1.10 Filling Fuel Tanks
A1.11 Waste Disposal Sites
A1.12 Stream Flow Measurement
Appendix B: CONVERSION FACTORS
REFERENCES AND FURTHER READING
SCIENTIFIC PAPERS
Index
Endorsement
End User License Agreement
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Guide
Cover
Table of Contents
Preface
Begin Reading
List of Illustrations
Chapter 1: INTRODUCTION
Figure 1.1
The hydrological cycle.
Figure 1.2
(a) A lower confined aquifer and an upper water table aquifer that includes low-permeability material supporting a perched water table. (b) Both confined and unconfined conditions can occur in the same aquifer.
Figure 1.3
How a conceptual model is developed from existing information and then gradually improved as field evidence is collected. Figure adapted from Brassington & Younger (2010) with permission of CIWEM.
Chapter 2: DESK STUDY
Figure 2.1
Different types of aquifer boundaries are shown in this diagram and discussed in the text.
Figure 2.2
This groundwater flow map for part of the Permian St Bees Sandstone aquifer in West Cumbria, England, was drawn at the beginning of the desk study stage to provide an early idea of groundwater levels before any boreholes had been drilled. Also see Figure 4.27. (Data by courtesy of the Environment Agency.)
Figure 2.3
Calculation of annual recharge.
Chapter 3: FIELD EVALUATION OF AQUIFERS
Figure 3.1
(a) Examples of sieves suitable for testing small samples in the field. (b) The three example curves show a uniform sand (1), poorly graded fine to medium-coarse sand (2) and well-graded silty sand and gravel (3), which are discussed in the text. (Photograph by courtesy of Endecotts Limited.)
Figure 3.2
An improvised method to assess grain-size distribution based on the principle that fine grains settle out in water more slowly than coarse grains.
Figure 3.3
Terms in the Darcy equation. See text for explanation.
Figure 3.4
Porosity in unconsolidated sediments varies with degree of sorting and shape of the grains. In consolidated rocks, porosity may be reduced by cement filling to pore spaces or increased by dissolution or by fracturing. See text for explanation of parts (a) to (f). (After Meinzer, 1923.)
Figure 3.5
Relationship between porosity, specific yield, specific retention and grain size applies to unconsolidated sediments only. Lines on these graphs are best-fit curves drawn through scattered points and are only approximate.
Figure 3.6 Hydraulic conductivities in metres per day for various rock types. (Adapted from Ground Water Manual by permission of the United States Department of the Interior.)
Figure 3.7
As a tracer flows through a rock (a), it divides each time an alternative pathway is reached. This process dilutes tracer concentration by mechanical dispersion and mixing. Graph (b) shows how concentration of a tracer varies with time as it flows past a particular point in an aquifer or emerges at a discharge point.
Figure 3.8
The concept of storativity. (a) Unit decline in head in a water table aquifer releases a volume of water equivalent to the specific yield. Under confined conditions (b), the unit decline in head releases a very small volume and the aquifer remains fully saturated.
Figure 3.9
Build up a picture of the aquifers in your study area based on the information you have collected or estimated using methods described in the text.
Figure 3.10
Regional flow (Q) through a sandstone aquifer can be calculated using Darcy's law.
Figure 3.11
The water table is drawn down into a cone of depression around a pumped well. Q, R, r, H and h are used in the equilibrium well equation (see text) to calculate hydraulic conductivity of the aquifer.
Figure 3.12
Thiem's steady-state equation can be solved graphically, as shown in this example.
Chapter 4: GROUNDWATER LEVELS
Figure 4.1
Main features of a commercially available dipper.
Figure 4.2
A home-made dipper comprising a length of door-bell cable and simple electronic circuit made from components available from any electronics supplier.
Figure 4.3
To measure groundwater levels where artesian conditions exist, either install a small chamber to take a pressure transducer/data logging system (a) or use a pressure gauge which is calibrated in metres head of water (b), or, for greater accuracy, fix a transparent plastic tube to the borehole (c) and measure the water level as a head (h) above the datum point.
Figure 4.4
Installation of a data logging system requires the data logger and a laptop or PC to program it, and this work can be done at the wellhead. (Photograph by courtesy of Van Essen Instruments Limited.)
Figure 4.5
Horizontal drum recorders are arranged so that the drum revolves in response to changes in water level, while the pen is driven by a clock.
Figure 4.6
Vertical drum recorders are arranged so that the pen moves in response to water-level changes, while the drum is rotated by a clockwork mechanism.
Figure 4.7
A surveyor's level (a) and how it is used (b and c).
Figure 4.10
A variety of head-works are found on boreholes and this diagram shows three examples.
Figure 4.8
Make a sketch plan to help locate the borehole in future and keep it with records for the site. Access difficulties and hazards such as bulls and dogs (or even a talkative farmer) can also be noted.
Figure 4.9
During your walkover survey you can spot a spring line by observing the vegetation and other signs. This spring line follows the contact between a sandstone and underlying mudstone and is marked by clumps of rushes or sedges, the start of a minor tributary to the main stream and a spring collection chamber. Most chambers look like a masonry or concrete box, partially buried and usually fenced round (see Figure 10.2).
Figure 4.11
Air pressure is occasionally used to measure water levels in abstraction boreholes, especially where access is restricted, such as the case in Figure 4.10c. These instruments frequently give erroneous readings, and it is best to avoid using them.
Figure 4.12
Relationships between the well or borehole construction and groundwater levels.
Figure 4.13
This borehole was drilled to a depth of 75 m near Morpeth in Northumberland in the Stainmore Formation at the top of the Namurian Group. Three piezometer pipes were added with response zones at 75–54 m, 38–29 m and 20–11 m. Each piezometer was surrounded by gravel and the rest of the borehole was filled with a sand/bentonite mixture. The left-hand drawing shows the relationship between the piezometer and geology, with different water levels in each piezometer. The water level in the highest piezometer is above that in the next one down; confusingly, that in the deepest one is above that in the highest one. The right-hand photograph shows the surface arrangement.
Figure 4.14
This series of hydrographs shows the record of groundwater levels measured in a piezometer nest installed in a borehole in the Sherwood Sandstone aquifer in west Lancashire, England, 1983–1991. The downwards vertical gradient indicates that the location is a discharge area. (Redrawn from Brassington (1992) by permission of CIWEM.)
Figure 4.15
How water flows through an idealised aquifer from recharge areas to discharge areas in valley bottoms. Flow lines are shown as solid lines, while equipotential lines are hatched. The effect of this flow system on water levels in wells gives decreasing elevations in recharge areas with depth and increasing elevations in discharge areas. . Note that the water level in adjacent boreholes is not the same if the depths are different. (Redrawn from Hubbert (1940) by permission of University of Chicago Press.)
Figure Box Figure 1.1
Three site investigations drilled in Bangor, North Wales, encountered a sequence of alluvial deposits that infill a glacial rockhead valley. Three water strikes were encountered in each borehole, with the water level rising inside the casing. In each case, after the deepest strike, the water level rose 15 m or more to rest just below ground level. (Data by courtesy of Shepherd Gilmour Environment Limited.)
Figure Box Figure 1.2
Differences in chemistry of water samples taken from the shallow and deep groundwater systems encountered by the site investigation boreholes shown in Box Figure 1.1, illustrated by Schoeller and Piper graphs. (Data by courtesy of Shepherd Gilmour Environment Limited.)
Figure 4.16
Components of drawdown and recovery in an abstraction borehole.
Figure 4.17
This example shows a nine-year record of a factory borehole, where rest and pumping-water levels were recorded at monthly intervals. (Data by courtesy of the Environment Agency.)
Figure Box Figure 2.1
The proposed cemetery is the field to the east of the Cricket Ground. The location of six piezometers is shown, as are groundwater contours at 0.1-m intervals. Contours show a flow direction to the northwest towards the Sherwood Sandstone aquifer where groundwater levels have been lowered by abstraction. (Data by courtesy of Newcastle-under-Lyme Borough Council.)
Figure 4.18
Groundwater levels measured at Chilgrove House since 1836 is believed to be the longest continuous record of water levels in the UK, and possibly the world. The well is located on head deposits over Seaford Chalk Formation in a branch off the generally dry Chilgrove valley about 10 km north of Chichester. It consists of a shaft some 0.9 m in diameter to 43.74 m with a 147 mm borehole, sunk to 62.03 m that is cased from the surface to the bored section. It was originally 41.15 m deep and was cleaned out and deepened to 43.74 m in 1855 after the drought of 1854. It was further deepened in March 1934 by a 147 mm diameter borehole to a depth of 62.03 m. The hydrograph is from 2010 to mid-2016. The solid line is the hydrograph and the dotted line is average values. The long-term maximum (blue) and minimum (pink) values are also shown. The hydrographs for the period generally show higher than average values in the winter periods and lower values during the summer months. The exceptions are the winter of 2011/2013 which has lower than average values and the end of 2012 that has higher values from recharge in the summer months. (Reproduced by permission of the British Geological Survey. © NERC. All rights reserved.)
Figure 4.19
Groundwater levels (a) fluctuate in response to changes in atmospheric pressure (b). In the lower graph the atmospheric pressure is shown in centimetres of water and the vertical scale has been reversed to make the comparison easier.
Figure 4.20
Barometric efficiency can be calculated by plotting water levels against atmospheric pressure (expressed as a column of water). The barometric efficiency is the slope of the straight line expressed as either a decimal or a percentage. (Note: based on data used in Figure 4.19.)
Figure 4.21
The three graphs are copies of recorder charts on observation boreholes and show various external influences on groundwater levels. In (a) the borehole is about 1.5 km from the coast; in (b) the borehole is located at a railway station; and in (c) the water levels are affected by an earthquake on the other side of the Earth. (Data by courtesy of the Environment Agency.)
Figure 4.22
Tidal effects can be assessed by comparing water-level readings from piezometers close to the coast.
Figure 4.26
An illustration of how groundwater contours and flow directions can be estimated from groundwater levels measured in three observation boreholes.
Figure 4.24
Construction of a groundwater contour map and flow net. (a) Values of groundwater levels are located on a plan, and key contours are plotted using techniques shown in Figure 4.23. In this example, contours at 22 m and 26 m were used. (b) Remaining contours are interpolated using these two contours as a guide. Flow-lines were sketched in, perpendicular to contour lines, starting on the 30-m contour at a spacing of 500 m.
Figure 4.25
Direction of groundwater flow at depth is not usually parallel to the water table; instead, water moves in a curved path, converging towards a point of discharge. Here two examples are shown, one in a deep aquifer (a) and the other in a shallow one (b).
Figure 4.26
Changes in groundwater levels can easily be studied if you construct a water-level change map.
Figure 4.27
Groundwater contour map for part of the St Bees Sandstone (Permian) aquifer in West Cumbria, England (see Figure 2.2). (Data by courtesy of the Environment Agency.)
Chapter 5: RAINFALL, SPRINGS AND STREAMS
Figure 5.1
A ‘standard’ Meteorological Office (UK) daily rain gauge consists of a brass cylinder that incorporates a funnel leading into a collection bottle. The volume of rainwater is measured each day using a standard measuring cylinder calibrated in millimetres depth of rainfall.
Figure 5.2
Examples of improvised rain gauges that should be sufficiently accurate for most groundwater studies.
Figure 5.3
Make notes of significant precipitation events with your record of rainfall data. No readings were taken for the 25th and 26th; instead the rainfall for these days has been included with that for the 27th as an accumulated total.
Figure 5.4
Use the guidelines contained in this diagram to position your rain gauge so that measurements are not affected by turbulence caused by the proximity of buildings or trees.
Figure 5.5
Thiessen polygons are constructed to calculate the total amount of rain falling on a catchment.
Figure 5.6
Main features of a British Standard evaporation tank (a) and a US Class-A evaporation pan (b).
Figure 5.7
An example of daily readings of rainfall and evaporation losses. Note asterisks mean not yet calculated.
Figure 5.8
Modify springs so that their flow can be measured with a jug and stopwatch by installing a temporary dam of stones and clay or concrete, through which the pipe projects for at least 200 mm.
Figure Box Figure 3.1
The tank (a) was made from 3-mm-thick galvanised-sheet steel bent to shape with welded joints, and a curved section was cut to hold the plastic pipe that carried the discharge. Effective height was limited by the change in floor level of 150 mm. In (b)the arrow shows the direction of flow. The stilling well was made from plastic water fittings and set with its base in a hole through the floor to create sufficient depth to insert a pressure transducer to record the weir tank water levels.
Figure 3.2a
View inside pipe shows the stainless-steel 90° v-notch plate with small water flow. The end plate can be seen at the back of the pipe; the hose carrying the mains water supply enters the picture from the right and can be seen on the left at the back of the pipe. Both the weir plate and end plate are fixed with a sealant adhesive.
Figure Box Figure 3.2b
General arrangement of the test rig set up on a stack of pallets to provide a firm horizontal platform, with the gaps between the boards modified to hold the pipe. A water supply carried in a hose enters the rear of two holes cut in the top of the pipe. The 10-L bucket was used as the calibrated vessel for flow measurements.
Figure Box Figure 3.2c
Data from lower flows were plotted on the graph and different trend lines were tried. The best fit was the power trend line with an relationship of 0.9975, which gave the formula .
Figure Box Figure 3.3a
(a) Arrangement in the drainpipe. The weir is on the right and the logger is held in a frame fixed to the left-hand wall of the chamber. The two cables are the power supply (black) and cable to the sensor (white/grey). In (b) the weir plate can be seen with water flowing over it in a nappe.
Figure 5.9
Example of a field record of spring-flow measurements. Time taken for the jug to fill to the 1-L mark is measured using a digital stopwatch. Measurements were repeated five times because of the apparent discrepancy between the first two readings. Average time is calculated and the reciprocal taken to give average spring-flow in litres per second.
Figure 5.10
Different ways that stream flow can be expressed. See text for details.
Figure 5.11
Four types of current meter in common use. In (a) the operator is using one of the current meters to gauge stream flow. The cup-type (b) has an impeller made up of six small cups that rotate on a horizontal wheel. The rotor type (c) has an impeller that looks like the propeller on an outboard motor. In both types, rate of rotation of the impeller is recorded by an electrically operated counter and is converted to velocity using a calibration chart. These instruments should be periodically recalibrated by a specialist firm. The acoustic current meter (d) uses ultrasonic Doppler technology to ascertain water flow velocity. The electromagnetic current meter (e) produces voltage proportional to velocity.(Reproduced by permission of Gurley Precision Instruments (image b); and of OTT Hydromet GmbH (images a, c, d and e.)
Figure 5.12
Stream flow is often measured by means of a current-meter gauging (a), where stream-flow velocities are measured at regular intervals across the stream, as shown in (b).
Figure 5.13
Field measurements to record during a stream-flow gauging, and how to use them to calculate flow. All symbols have the same meaning as Figure 5.12. Record all depths and distances in metres. Some instruments automatically convert number of revolutions into velocity; otherwise use tables supplied with the instrument.
Figure 5.14
This example shows how field data have been used to calculate stream flow using the method given in Figure 5.13. In this case, the current meter only recorded revolutions and not velocities. Velocity measurements were taken at half the depth and so, once total flow had been calculated, it was corrected by multiplying by 0.95.
Figure 5.15
It is important that a v-notch weir is made to the correct specification for accurate measurements to be achieved (see main text). The general arrangements shown in (a) apply to the three types of v-notch shown in (b).
Figure 5.16
Installation of a weir plate.
Figure 5.17
A stage–discharge graph shows the relationship between stream flow and stream-water level at a particular point.
Figure 5.18
A continuous record of stream level is made by a temporary installation of a water-level recorder or data logger system.
Figure 5.19
Relationship between spring flow and rainfall is easily discovered if records are plotted on the same time scale.
Figure 5.20
A base flow graph can be constructed from a semi-logarithmic plot of stream flow on the log-scale against time on the linear scale. Rate of base flow recession is a constant, which produces a series of parallel lines as shown. The groundwater component of stream flow is represented by the area on the graph beneath these straight lines.
Chapter 6: PUMPING TESTS
Figure 6.1
An electrical submersible pump hung on a bolted-flange jointed rising main and suspended in a borehole on pipe clamps that rest on top of the borehole casing. Alternatives include hanging the pump on a flexible rising main that comes in one length to ensure that the pump is at the predetermined depth or where small pumps are involved using a small-diameter plastic pipe, again in one length. The electrical cable is tied at intervals to the main. A dip tube is installed which extends to below the pump intake.
Figure 6.2
Air-lift pumping uses the sort of equipment shown here.
Figure 6.3
Discharge from a pumping test can be measured using a weir tank such as those shown here (for explanation of parts (a) to (c) see text). The wooden tank in photograph (d) has been made to measure small flows. It has five sections; the first four are separated by baffles that either extend from the base or are suspended above the base of the tank. The fourth and fifth sections are separated by a ¼ 90
o
weir plate, over which the water flows to discharge into the fifth section, where it is carried to a discharge point through a hose.
Figure 6.4
Arrangement for controlling and measuring pump discharge during a pumping test.
Figure 6.5
These field sheets are used to record the water level and discharge measurements taken during pumping tests. NGR stands for National Grid Reference, the UK system of map referencing.
Figure 6.6
Data from a step-drawdown test have been used to plot a specific capacity curve that defines borehole performance. Diagram (a) shows the water level decline with each step. In (b) two specific capacity curves have been plotted, with the second one produced from a second test carried out at a later date. It can be seen that the well performance has decreased with a greater drawdown for the same pumping rate as shown in (c).
Figure 6.7
Planning a pumping test to assess the environmental impact of a proposed abstraction requires consideration of local hydrogeological factors such as shown here.
Figure 6.8
The Cooper–Jacob method of pumping test analysis uses a graph of drawdown on a normal scale against time on a semi-logarithmic scale and is a useful preliminary way of examining pumping test results.
Figure 6.9
Data from a pumping test at Roe Head Mills at a rate of approximately , with the effects of a barrier boundary in the later data.
Figure 6.10
Water-level measurements taken during a 7-day pumping test at a rate of show several boundary effects.
Figure 6.11
A graphical method to solve Bierschenk's equation.
Figure 6.12
Data from a pumping test are plotted on a semi-log scale to solve the Cooper–Jacob equation.
Figure 6.13
Recovery data from the same pumping test as in Figure 6.12.
Figure 6.14
Shape factors () for calculating hydraulic conductivity from slug tests using the Hvorslev equation (where is length of test section in metres and is diameter of the test borehole at the water surface in metres). (After Hvorslev 1951.)
Figure 6.15
In Hvorslev's method the basic time lag () is determined graphically as shown.
Figure 6.16
A double packer assembly hung on pipe and installed in a borehole. (Reproduced from Brassington and Walthall, 1985 by permission of the Geological Society.)
Chapter 7: GROUNDWATER CHEMISTRY
Figure 7.1
Small electrical submersible pumps can be used for sampling. Photograph (a) shows the control box and delivery hose for a Grundfos MP1 sample pump that is down the borehole. Photograph (b) shows the pump after it has been retrieved from the borehole.
Figure 7.2
The operator is using an inertial pump driven by a portable generator to operate the pump. (Photograph by courtesy of In-Situ Europe Ltd.)
Figure 7.3
A sample of groundwater can be obtained from a predetermined depth using a depth sampler.
Figure 7.4
This sampler uses air pressure to control the depth at which water is drawn into the sampler, thereby eliminating possible contamination from water flowing through it as it is lowered down the borehole. (Photograph by courtesy of Solinst Canada Ltd.)
Figure 7.5
On-site measurements of temperature, specific electrical conductance (SEC), alkalinity, pH, dissolved oxygen (DO) and redox potential (Eh) were taken at a water utility sampling point in the Chalk in Hampshire. Alkalinity was measured by titration against H
2
SO
4
and was reported as HCO
3
. The pH, Eh and DO were measured in a flow cell to restrict aeration and were monitored until stable readings were obtained. (Photograph by courtesy of the Environment Agency and the British Geological Survey. © NERC. All rights reserved.)
Figure 7.6
The IsoFlask sample bag comes empty except for a biocide. It is filled using the one-off-use sample tube. (Photograph by courtesy of Isotech Laboratories, Inc. (A Weatherford Company), Champaign, Illinois, USA.)
Figure 7.7
This series of photographs illustrates the way that noble gases are sampled. Water is passed through the small-diameter copper tube in (a) and then clamps (b) at each end are fastened, with the one at the discharge end being first. The sample is preserved in the tube at a high pressure (>3 bar) as in (c). (Photographs by courtesy of the Department of Geology and Geophysics, University of Utah, Salt Lake City, Utah, USA.)
Figure 7.8
The method of sampling for CFCs is shown in (a) and for SF6 in(b). Note the same equipment can be used for both samples, although only CFCs need to be sampled underwater. (Figure redrawn from the USGS website with permission.)
Figure 7.9
The most commonly used BART test kits are Iron Related Bacteria (IRB-BART – red top), Sulphate Reducing Bacteria (SRB-BART – black top) and Slime Forming Bacteria (SLYM-BART – green top). The samples in the picture were observed for 8 days. The IRB-BART shows aggressive iron-related bacteria to be present; SLYM-BART shows the presence of slime-forming bacteria; and SRB-BART shows little sulphate-reducing bacteria, although the cloudy solution indicates the presence of anaerobic bacteria.
Figure 7.10
In the Schoeller graph the relationship between two chemical constituents in different water samples is shown by the slope of the straight lines connecting these constituents. In this example, the chemistry of the two springs is very similar, whereas the water from the borehole is quite different, indicating that it penetrates an aquifer separate from the one supporting the springs.
Figure 7.11
In Piper's trilinear method, concentrations of cations and anions are plotted as the percentage of the total of each when expressed in milli-equivalents. The grouping on the central diamond-shaped field shows up waters that have a similar chemical composition. Data used in this diagram are the same as those used in Figure 7.10.
Chapter 8: RECHARGE ESTIMATION
Figure 8.1
Determination of actual recharge from potential recharge (HER) with different types of drift. (Reproduced by permission of CIWEM from Rushton et al. (1988).)
Figure 8.2
How aquifer recharge may percolate through low-permeability layers above a confined aquifer.
Chapter 9: SPECIALIST TECHNIQUES
Figure 9.1
The main features of a shell and auger rig. Tools shown are a clay cutter, bailer and chisels.
Figure 9.2
A lorry-mounted percussion rig and the common tools that are used.
Figure 9.3
The main features of a lorry-mounted rotary drilling rig.
Figure 9.4
Down-hole geophysical measurements being taken. (Photograph by courtesy of European Geophysical Services Limited.)
Figure Box Figure 4.1
Vertical profiles of caliper (Cal), natural gamma (Gam), fluid temperature (T), differential temperature (DT), fluid conductivity (EC25), differential conductivity (DC) and comments on features seen during CCTV inspection.
Figure Box Figure 5.1
Location of sites discussed in the text, including the three injection points and 18 monitoring points in relation to the geology and drainage system. Monitoring points are mainly springs at the alluvium/limestone contact, with a few that act as controls.
Chapter 10: PRACTICAL APPLICATIONS
Figure 10.1
A vertical profile of EC measurements on water samples taken at each rod change in the borehole. (Reproduced from Brassington F.C. and Taylor R. (2012) by permission of the Geological Society.)
Figure 10.2
During a pumping test on a borehole in a sandstone aquifer, water-level measurements were made on the borehole. Drawdown data were plotted on a semi-log graph as shown, with the line extended to 1,000,000 minutes (almost 2 years) to predict a long-term drawdown of 18 m.
Figure 10.3
Protect a spring source with a catch pit that is large enough to capture the entire flow and incorporate the features shown here.
Figure 10.4
Field examples of exploitation of an unconfined aquifer of limited saturated thickness: (a) vertical well with submersible pump in gravel aquifer, (b) large-diameter well in weathered zone, (c) wellpoints in sand dune aquifer, (d) horizontal well in sand dune aquifer. (Reproduced from Rushton and Brassington (2016) with permission of Copyright © 2015, Springer-Verlag Berlin Heidelberg.)
Figure 10.5
A data set can be extended by comparison with a longer data set. This method is used here to determine the expected highest groundwater levels at the proposed cemetery site.
Figure 10.6
Before and after conditions show how a large excavation into an aquifer can lower the water table by increasing the available aquifer storage. The impact may be greater if the quarry is dewatered.
Figure 10.7
Monitoring boreholes around a sandstone quarry are shown in (a), together with groundwater contours in metres above Ordnance Datum (approximately sea level). In (b) the hydrographs are seen, with those below the site having a greater fluctuation than those that lie above it where the fluctuations appear to be almost non-existent. The actual fluctuations can be seen in (c) when the hydrographs are plotted on a larger scale. The difference between the hydrographs is explained by the presence of the large quarry void that pulls down the water levels above the site and does not affect those below it so much.
Figure 10.8
A road cutting has been excavated through a hill formed from an aquifer with springs that discharge at A and B (a). Once the cutting was excavated below the water table, it was kept dry by groundwater being diverted along trench drains installed on both sides (b). The flow of both springs is approximately halved with their catchment areas reduced by about 50%. (Note: ditches are usually installed at the top of cuttings to help maintain slope stability, but these have been omitted from the diagram.)
Figure 10.9
The piled foundations of high-rise buildings may be sufficiently dense to reduce the effective cross-sectional area of a shallow aquifer, thereby reducing transmissivity. This will cause groundwater levels to rise on the ‘upstream’ side of the buildings, and alter the flow pattern round it which might affect the yield of nearby wells.
Figure 10.10
Ditches and drains can provide a route for groundwater discharge that lowers the water table, with potential impacts on local spring and well supplies.
Figure 10.11
These sketches show how wetlands are formed and rely on a constant water supply.
List of Tables
Chapter 1: INTRODUCTION
Table 1.1
Template for planning the contents of a report
Chapter 2: DESK STUDY
Table 2.1
Average water requirements for various domestic purposes, agricultural needs and manufacturing processes
Table 2.2
Checklist for planning a fieldwork programme
Chapter 3: FIELD EVALUATION OF AQUIFERS
Table 3.1
Typical values of porosity and specific yield for a range of aquifer materials
Table 3.2
Classification of rock types in terms of permeability
Table 3.3
Values of C in Hazen's formula
Chapter 4: GROUNDWATER LEVELS
Table 4.1
Standard ranges of pressure transducers
Table 4.2
Checklist for tools and equipment
Table 4.3
Headings for well catalogue
Table Box Table 1.1
Chapter 5: RAINFALL, SPRINGS AND STREAMS
Table 5.1
Flow over thin-plate weirs in litres per second
Table 5.2
Maximum flows for accurate measurement with different methods
Chapter 6: PUMPING TESTS
Table 6.1
Checklist for pumping test planning
Table 6.2
Checklist for pumping test equipment
Table 6.3
Optimum depth of submergence for airlift pumping
Table 6.4
Frequency of water-level readings during pumping tests
Table 6.5
Size of survey areas and duration of pumping tests
Table 6.6
Summary of results from the test at Paramali, Cyprus
Chapter 7: GROUNDWATER CHEMISTRY
Table 7.1
Analytical suites for groundwater quality assessment
Table 7.2
Relationship between conductivity of solutions at different temperatures to a standard of 20°C
Table 7.8
Protocol for sampling from a well using an electrical submersible sample pump
Table 7.3
Checklist to prepare for groundwater sampling
Table 7.4
Checklist for sampling equipment
Table 7.5
Protocol for sampling from springs
Table 7.9
Protocol for sampling from a well using an inertial pump
Table 7.10
Information to be recorded in the field for groundwater samples
Table 7.11
Selected chemical parameters to determine the potability of a water supply
Table 7.12
Conversion factors from milligrams per litre to milli-equivalents
Table 7.13
Conversion factors for various ions and analytical units
Chapter 8: RECHARGE ESTIMATION
Table 8.1
Water-balance equation
Table 8.2
Components of the water-balance equation
Table 8.3
Summary of the relationship between evaporation losses from open water and those from bare soil, grassland and chalk soils
Table 8.4
Recharge factors proposed by Rushton et al. (1988)
Chapter 9: SPECIALIST TECHNIQUES
Table Box Table 4.1
Table 9.1
Geophysical tools used in hydrogeology
Table Box Table 5.1
Chapter 10: PRACTICAL APPLICATIONS
Table 10.1
Potential contaminant release in kilograms from a single 70-kg burial
Table 10.2
Calculated contaminant loading
Appendix A: GOOD WORKING PRACTICE
Table A.1
Code for minimum impact of fieldwork on the countryside
The Geological Field Guide Series
Field Hydrogeology, Third edition
, Rick Brassington
Basic Geological Mapping, Fourth edition
, John Barnes
The Field Description of Metamorphic Rocks
, Norman Fry
The Mapping of Geological Structures
, Ken McClay
Field Geophysics, Third edition
, John Milsom
The Field Description of Igneous Rocks
, Richard Thorpe and Geoff Brown
Sedimentary Rocks in the Field, Third edition
, Maurice Tucker
Field Hydrogeology
FOURTH EDITION
Rick Brassington
Consultant Hydrogeologist Warrington, UK
This edition first published 2017
© 2017 John Wiley & Sons Ltd
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ISBN: 9781118397367
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To my wife Sandra Brassington.
PREFACE
I was asked to revise my book by Rachael Ballard, my then Wiley editor, both to update it and to produce material for an e-book edition; this I hope I have done. As always, the book is intended as a hands-on guide to field methods in hydrogeology, explaining what techniques are needed and how to carry them out. The book's layout mirrors the logical sequence for the development of a conceptual model to understand the hydrogeology of an area, with the associated field studies needed to validate that understanding. Processing and interpreting the information collected during a data-gathering exercise is necessary to develop your conceptual understanding of a particular site and, consequently, these tasks have also been included. This fourth edition updates the information on the most recent field methods and instruments, although my practical approach includes suggestions on improvising measurements when specialist equipment is not available or cannot be used. I have included an additional case history, bringing the total to five, again using my projects as inspiration. They illustrate how field measurements are interpreted and the interrelationships between different aspects of groundwater systems, as well as how to take measurements in difficult situations.
Although the book is primarily aimed at graduate and undergraduate earth science students, earlier editions have also proved useful to many others. Consequently, I have rearranged the contents of Chapter 10, moving some to Chapter 1, and have included how to carry out a borehole prognosis, despite it being a desk-top study rather than fieldwork. There is a greater emphasis on abstraction systems, including those from shallow aquifers; I have included geothermal systems, which are growing in popularity; have rewritten the section on the impact of large excavations on groundwater systems; and included a short section on soakaway systems. However, the underlying theme of the book continues to be the fundamental importance of the geology of an area in trying to understand its hydrogeology, and the significance of field observations in developing this understanding. Both are essential for reliable hydrogeological interpretation, so make sure that they are always a central part of your work.
Rick Brassington 2016
ACKNOWLEDGEMENTS
A large number of people have provided helpful comments and guidance during the planning and preparation of this revision and I regret that it is not possible to name them all. In particular, I would like to thank Kim Beesley, George Darling, Noelle Odling and Ken Rushton for their constructive criticism and helpful suggestions for this fourth edition; and in Wiley I would like to thank Rachael Ballard, Executive Commissioning Editor, and Delia Sandford, Managing Editor, for their patience with me, and Nithya Sechin for her help and patience in putting together my draft. I am also indebted to several of my clients for permission to use data from projects I have completed for them, including those that asked for the site details to remain anonymous. As ever, I am especially grateful to my wife Sandra for her loving support and patience.
Grateful acknowledgement is made for the following illustrative material used in this book as follows:
Figures 1.3, 4.14 and 8.1, and Table 6.5: CIWEM; Figures 2.2, 4.17, 4.18, 4.21, and 4.27, and Tables 2.1 (part), 6.5 (part), and 10.1: Environment Agency © Environment Agency; Figure 3.1a: Impact Test Equipment Ltd; Figures 3.4 and 7.8, and Table 3.1 (part): US Geological Survey; Table 3.2: Dept. of Economic and Social Affairs, Groundwater in the Western Hemisphere, United Nations (1976); Figure 3.6: redrawn from the Groundwater Manual, US Department of the Interior (1995) and used with permission of the Bureau of Reclamation; Table 4.1: Cambertronics Ltd; Figures 4.4 and 7.2: In-Situ Europe Ltd; Figure 4.15: redrawn from Hubbert (1940); Figures 4.18 and 7.5: British Geological Survey © NERC All rights reserved; Figures 6.16 and 10.1, and Table 3.1 (part): Geological Society of London; Figure 6.14: US Army Corps of Engineers; Figure 7.4: Solinst Canada Ltd; Figure 7.6: Isotech Laboratories; Figure 7.7: Department of Geology and Geophysics, University of Utah; Figure 9.4: European Geophysical Services Ltd; Figure 10.4: Springer-Verlag Berlin Heidelberg, Copyright © 2015; Figure 10.8: redrawn from Brassington (2014) by permission of Extractive Industry Geology Conferences Ltd; Box Figures 1.1 and 1.2 and the data for Case History 1: Shepherd Gilmour Environment Ltd; Box Figure 2.1, the data for Case History 2, and the example used in Section 10.5.1: Newcastle-under-Lyme Borough Council.
Chapter 1INTRODUCTION
Groundwater provides an important source of drinking water over much of the world. It also has the fundamental importance of maintaining river and stream flows during periods without rain and also supporting wetland sites. Groundwater is under threat worldwide from overabstraction and by contamination from a wide range of human activities. In many countries, activities that may impact on groundwater are regulated by government organisations, which frequently require hydrogeological investigations to assess the risks posed by new developments.
Pumping from new wells may reduce the quantities that can be pumped from others nearby, cause local spring flows to dwindle, or dry up wetlands. The hydrogeologist will be expected to make predictions on such effects and can only do so if he or she has a proper understanding of the local groundwater system based on adequate field observations. It is equally important to evaluate groundwater quality to ensure that it is suitable for drinking and for other uses. Groundwater commonly provides the flow path that allows pollutants to be leached from industrially contaminated sites, landfills, septic tanks, chemical storage areas and many more. Hydrogeological studies are needed to define groundwater systems in order to prevent such contamination or manage its clean-up. This book is concerned with the field techniques used by hydrogeologists to evaluate groundwater systems for any or all of these purposes and with the primary or initial interpretation of the data collected in the field.
1.1 Groundwater Systems
Groundwater is an integral part of the hydrological cycle, a complex system that circulates water over the whole planet; this is illustrated in Figure 1.1. The hydrological cycle starts as energy from the sun evaporates water from the oceans to form large cloud masses that are moved by the global wind system and, when conditions are right, precipitate as rain, snow or hail. Some of it falls onto land and collects to form streams and rivers, which eventually flow back into the sea, from where the process starts all over again. Not all rainfall contributes to surface water flow, as some is returned to the atmosphere by evaporation from lakes and rivers, from soil moisture and as transpiration from plants. Water that percolates through the soil to reach the water table becomes groundwater. In thick aquifers, groundwater at depth is below the depth of freshwater circulation and is saline, often with a higher electrical conductivity than seawater. The same is true for groundwater down dip from the outcrop of an aquifer. Groundwater flows through the rocks to discharge into either streams or rivers. In coastal areas, groundwater discharges into the sea, and the aquifer contains seawater at depth. The volume of water percolating into the aquifers defines the groundwater resources that both support natural systems and are available for long-term water supply development. In most groundwater studies it is necessary to consider the other components of the cycle as well as the groundwater itself in order to understand the groundwater system. Consequently, hydrogeological investigations usually include a range of field measurements to assess these parameters.
Figure 1.1The hydrological cycle.
Groundwater flow through saturated rock is driven by a hydraulic gradient, which, in unconfined aquifers, is the water table. Rocks that both contain groundwater and allow water to flow through them in significant quantities are termed aquifers. Flow rates that are considered as significant will vary from place to place and also depend on how much water is needed. Water supplies to individual houses require small groundwater flows compared to wells supplying a town. In pollution studies, even small groundwater flow rates may transport considerable amounts of contaminant over long periods of time. A critical part of the definition is that the rock allows a flow of water, rather than simply containing groundwater. Some rocks such as clays have a relatively high water content, although water is unable to flow through them easily. Other rocks may not be saturated but still have the property to permit water to flow, and therefore should be regarded in the same way as an aquifer, a clear example being the part of an aquifer formation that lies above the water table.
Unless groundwater is removed by pumping from wells, it will flow through an aquifer towards natural discharge points. These comprise springs, seepages into streams and rivers, and discharges directly into the sea. The property of an aquifer that allows fluids to flow through it is termed permeability, and this is controlled largely by geological factors. Properties of the fluid are also important, and water permeability is more correctly called hydraulic conductivity. Hydrogeologists often think of hydraulic conductivity on a field scale in terms of an aquifer's transmissivity, which is the hydraulic conductivity multiplied by the effective saturated thickness of the aquifer.
In both sedimentary rocks and unconsolidated sediments, groundwater is contained in and moves through the pore spaces between individual grains. Fracture systems in solid rocks significantly increase the hydraulic conductivity of the rock mass. Indeed, in crystalline aquifers of all types, most groundwater flow takes place through fractures, and very little, if any, moves through the body of the rock itself. Some geological materials do not transmit groundwater at significant rates, while others only permit small quantities to flow through them. Such materials are termed aquicludes and aquitards, respectively, and although they do not transmit much water, they influence the movement of water through aquifers. Very few natural materials are completely uniform and most contain aquiclude and aquitard materials.
Figure 1.2 shows how the presence of an aquiclude, such as clay, can give rise to springs and may support a perched water table above the main water table in an aquifer. The top diagram (Figure 1.2a) shows a lower confined aquifer and an upper water table aquifer. The upper aquifer includes low-permeability material that supports a perched water table. The diagram shows the rest-water levels in various wells in both aquifers. Figure 1.2b shows how both confined and unconfined conditions can occur in the same aquifer. In zone A, the aquifer is fully confined by the overlying clay and is fully saturated. The groundwater in this part of the aquifer is at a pressure controlled by the level of water at point p, and water in wells would rise to this level above the top of the aquifer. In zone B, the overlying clay will prevent any direct recharge, although it is unconfined, like zone C. The aquifer in zone C is unconfined and receives direct recharge. Seasonal fluctuations in the water-table levels will alter the lateral extent of zone B along the edge of the aquifer. It is likely to be at a minimum at the end of the winter and at its greatest extent in the autumn, before winter recharge causes groundwater levels to rise.
Figure 1.2(a) A lower confined aquifer and an upper water table aquifer that includes low-permeability material supporting a perched water table. (b) Both confined and unconfined conditions can occur in the same aquifer.
Where impermeable rocks overlie an aquifer, the pressure of the groundwater body can be such that the level of water in wells would rise above the base of the overlying rock (i.e. the top of the aquifer). In such instances the aquifer is said to be confined. Sometimes this pressure may be sufficiently great that the water will rise above the ground surface and flow from wells and boreholes without pumping. This condition is termed artesian flow, and both the aquifer and the wells that tap it are said to be artesian.
A groundwater system, therefore, consists of rainfall recharge percolating into the ground down to the water table, and then flowing through rocks of varying permeabilities towards natural discharge points. The flow rates and volumes of water flowing through the system depend upon the rainfall, evaporation, the geological conditions that determine permeability, and many other factors. It is this system that a hydrogeologist is trying to understand by carrying out field measurements and interpreting the data in terms of the geology. The four key factors in achieving a successful investigation are to understand the geology; to interpret the groundwater-level data in terms of the three-dimensional (3D) distribution of heads that drive all groundwater flow systems; to remember that groundwater and surface water systems are interdependent; and to use a structured iterative approach to developing your understanding of the groundwater system you are investigating.
1.2 Conceptual Model
The foundation of all hydrogeological investigations is to gather sufficient reliable information to develop an understanding of how a particular groundwater system works. Such an understanding is usually called a conceptual model and comprises a quantified description encompassing all aspects of the local hydrogeology. Consequently, it is necessary for you to think about the way you will develop a conceptual model at the beginning of each project and as the basis of planning the work that is needed.
Although inexorably linked, the activities that form a hydrogeological investigation and the methodology of developing a conceptual model are not exactly the same. The actions at each step of a hydrogeological investigation are generally focused on collecting information, whereas the emphasis in developing a conceptual model is the interpretation of data as they are collected to identify additional information needed to complete the conceptual understanding. A typical hydrogeological investigation can be divided into a number of separate parts, each building on the previous one to eventually achieve an adequate understanding of the system being studied. It will always be necessary to tailor the details of an investigation to the needs of each particular study, although the majority of investigations are made up of the following phases:
Desk study – the existing available information is assembled to provide an early opportunity to get a ‘feel’ for the groundwater system and start the conceptual modelling process.
Walkover survey – it is important to get to know the study area at first hand, so that you can plan your fieldwork programme.
Exploration – may include drilling boreholes, pumping tests and geophysical investigations.
Monitoring programme – defines the variation in groundwater levels, groundwater chemistry, rainfall, spring and stream flows, and so on, both across the area and seasonally.
Data management – a systematic way of noting data in the field and examining it as it is collected to determine its reliability and if it represents the groundwater in your study area. It is likely that you will store the field data electronically, so do not forget to make regular back-ups.
Water balance – quantifies the volumes of water that are passing through the groundwater system. Computer simulations may be used in this process to help define recharge and flows through the aquifer.
Completion of the conceptual model and providing a quantified description of the groundwater system. The quantified aspect is important as it defines things like well yields, groundwater flow rates, recharge quantities and the groundwater chemistry.
A framework for developing a conceptual model as a series of steps was proposed by Brassington and Younger (2010) and is illustrated in Figure 1.3. The steps follow the logical sequence taken in developing a conceptual model that defines the information sources, activities and review process required along the way, including an audit trail to record all the information that relates to your project. The repetition in the review process is an essential element that ensures the data collection and field work programme are sufficient to enable you to draw meaningful conclusions from your work. The steps summarised in Figure 1.3 are explained in more detail below, with details of how to collect and interpret the data given in subsequent chapters of this book.
Figure 1.3How a conceptual model is developed from existing information and then gradually improved as field evidence is collected. Figure adapted from Brassington & Younger (2010) with permission of CIWEM.
1.2.1 Step 1 – defining the objectives
You should define the purpose of each investigation before starting it, so that you focus on all the key questions that need answering as you design the field investigations to provide all the necessary data. In most cases the objectives should be set out in writing and agreed with your boss, the client, the regulator or any other people with interests in the outcomes of the project. If you work as a consultant, part of this objective setting may be contained in the proposal that you send to the client before you were appointed to undertake the project.
1.2.2 Step 2 – defining the geology
The geology of an area controls its hydrogeology and so it is essential to understand the types of rocks present in the area of interest, their lithologies and their structural relationships. The information can be derived from existing geological maps and reports, although sometimes
