Water Supply Boreholes Research Articles

Microbiological assessment of private drinking water supplies in Co. Cork, Ireland

The microbiological quality of 75 private drinking water supply boreholes in Co. Cork, Ireland was assessed in order to determine the incidence of contamination and the potential pathways of such contamination. Microbiological analysis was carried out using the membrane filtration technique for the recovery of thermotolerant (faecal) coliforms. The sanitary protection of the supplies was evaluated by means of systematic inspections and subsequent qualitative sanitary risk assessment. Almost a quarter of all supplies investigated (24%, n = 18) was found positive for thermotolerant coliforms. Weather conditions had a significant impact on microbiological water quality, increasing both contamination incidence and gross contamination frequency. Over half of the supplies had nine or more sanitary hazards and most had rudimentary sanitary protection measures at the head of the borehole. These low sanitary protection measures suggest that boreholes can pose a significant hazard to valuable groundwater resources by providing direct contamination routes.

Anthropogenic Activities-Implications for Ground Water Resource in Okrika, Rivers State, Nigeria

This work is an attempt to establish aquifer distribution in the indicated area as an aid to locating possible and suitable sites to drill boreholes for safe, portable and sustainable water supply for the ever-growing population and industries in the area, and the vulnerability of this body of water to pollutants as a result of human and industrial activities in the area. Data collected from vertical electrical sounding were used to interpret, both laterally and vertically, varying successions of high and low resistive geoelectric layers throughout the area of study to establish the depth, thickness and lateral extent of an aquifer, and also to determine the layering of the study area down to the depth of interest; thus, to delineate the aquifer distribution of the area. To ensure the safety status of groundwater of the area, a chemical analysis of three pollutants (heavy metals) of interest {Lead (Pb), Copper (Cu), and Nickel (Ni)} was carried out on sixty soil samples collected randomly from ten locations at various depths from the ground surface to a depth of 25m to determine their total concentration in the soil at ground level and their degree of leaching towards the groundwater of the area. The energy Dispersive XRay Fluorescence (EDXRF) technique was used to analyze and determine the total concentration of the pollutants in the soil samples. The results show that there is good aquifer distribution laterally across the study area with aquifer thickness of between 50m to 60m. The groundwater resource of the area is less vulnerable to pollutants because of the presence of a thin layer of organic matter and clay deposits that adsorb the pollutants of interest and minimize the leaching of the pollutants towards the saturated zone.

Using environmental tracers to assess the extent of river–groundwater interaction in a quarried area of the English Chalk

The Swanscombe area of Kent, SE England represents a typical example of a heavily quarried Chalk area currently undergoing re-development. Because the Chalk is also an important aquifer, a good understanding of groundwater movement is required if environmental impacts are to be minimised and the water resource maximised. In particular, the nature of the relationship between the River Darent and groundwater in the Swanscombe Chalk Block requires better characterisation. Here, ‘environmental tracers’ in the form of ambient concentrations of stable isotopes, chlorofluorocarbons (CFCs), sulphur hexafluoride (SF6) and tritium (3H) are used to investigate this and other aspects of groundwater movement in the vicinity of the quarries. Stable isotopic contrasts indicate little evidence for widespread river infiltration to the regional Chalk aquifer, although stable isotope and 3H data suggest that 20–35% of the abstraction by river-valley public water supply boreholes may be derived from the river. The CFCs, while present at above-modern concentrations in almost all groundwaters, can be used as tracers, indicating basically S–N flowpaths in the area south of the quarries, though sub-karstic conduits associated with areas of Palaeogene cover add a level of uncertainty at the local scale. Simple piston flow residence times based on SF6 range from 1 to 17 a, but the data are probably better interpreted in terms of mixing between varying amounts of modern recharge derived from the south and deeper stored groundwater. The information gained from environmental tracers can therefore contribute to effective resource management.

The potential use of hydrogen peroxide in water well rehabilitation

AbstractA water supply borehole in the Sherwood Sandstone aquifer in Warrington, UK was found to be infested with iron bacteria that resulted in large ochreous deposits and damaged the pump. Before the pump was replaced, the borehole was treated using hydrogen peroxide. Comparison of the borehole condition seen in CCTV surveys carried out before and after treatment shows that previously observed bacterial growths had been removed. A specific capacity curve was constructed from step test data and used to assess the borehole yield under operational conditions. This showed that the iron bacteria had increased drawdown by some 20% and that the treatment had restored the previous yield characteristics. The improvement is thought to be due to a mechanical scrubbing effect caused by the vigorous release of oxygen bubbles during the decay of the peroxide.

Hydrofracturing water boreholes in hard rock aquifers in Scotland

Hydrofracturing of new public water supply boreholes in Precambrian crystalline bedrock in Scotland has increased borehole yields by at least one order of magnitude, and made the difference between borehole abandonment and success. In many upland rural areas of the UK, low-productivity aquifers are an important resource for small public water supplies. Where a borehole in low-productivity crystalline rocks proves too low yielding for its designed purpose, hydrofracturing is a cost-effective means of enhancing yield.

Aspects of the lateral and vertical resolution of surface electroseismic data with implications for groundwater exploration in fractured Karoo rocks

Horizontal bedding-plane fractures are of prime importance for the drilling of successful water-supply boreholes in Karoo rocks, but usually have very localized occurrences and small aperture widths. Geophysical methods conventionally used for groundwater exploration in Karoo rocks are unable to detect these fractures. Electroseismic (ES) methods make use of the fact that electromagnetic waves are radiated when seismic waves cause fluid flow across interfaces between porous media of different electrokinetic properties. Since the electrokinetic contrast between a fluid-filled fracture and its host is likely to be high, ES signal generation may occur at both the top and bottom interfaces of the fracture. The ability of surface ES methods to detect and resolve the fractures depends on the lateral and vertical resolution of ES data. The ES Fresnel zones are larger than their seismic equivalents and the lateral resolution of ES data is correspondingly poorer. Seismic velocity increases with depth have an additional negative impact on the lateral resolution of ES data. Assuming that a fracture has a measurable surface ES response, a simplified model shows that the response from a localized fracture may be observed at surface positions laterally displaced from the fracture. The presence of large localised unfractured areas occurring within fractured areas may not be detected at all. Rayleigh’s vertical resolution criterion applied to electroseismic data requires that an embedded thin layer have a minimum thickness of half the dominant wavelength of the seismic wave. Since the Biot slow wave has a much smaller wavelength than the Biot fast wave, it would seem that the limits of vertical resolution are determined by the dominant wavelength of the slow wave. The dissipative nature of the slow wave, however, may cause the practical limit of vertical resolution to be more dependent on the wavelength of the fast wave. The detection of a thin embedded layer depends on the conditions of constructive and destructive interference of signal generated at its top and bottom interfaces. For both the fast and slow wave a thin bed with a thickness less than a quarter of the dominant wavelength results in a total ES response that is weaker than the response from the top interface alone. For both fast and slow pressure waves this thickness is much larger than the aperture width of the bedding-plane fractures in Karoo rocks, and detection of these fractures with surface ES methods seems unlikely.

The potential for methane emissions from groundwaters of the UK

Methane (CH 4) is only a trace constituent of the atmosphere but an important greenhouse gas. Although groundwater is unlikely to be a major source of atmospheric CH 4, its contribution to the CH 4 budget of the UK has up to now been poorly characterised. Groundwater CH 4 concentrations have been measured on 85 samples from water-supply boreholes and a further eight from other miscellaneous water sources. Concentrations in abstracted groundwaters ranged from <0.05–42.9 μg/l for Chalk, <0.05–22 μg/l for the Lower Greensand, 0.05–21.2 μg/l for the Lincolnshire Limestone and from <0.05–465 μg/l for the Triassic sandstone. Having the largest abstraction volume, the Chalk is likely to be the main UK groundwater contributor to global CH 4 emissions. A calculation to estimate the total emissions of CH 4 from water-supply groundwater sources based on the median and the maximum CH 4 concentrations gave values of 2.2×10 −6 and 3.3×10 −4 Tg/year. Estimates show groundwater contributes a maximum of 0.05% of all UK CH 4 emissions and a further two orders of magnitude less in terms of the global CH 4 budget. Other groundwater sources such as inflows to tunnels may have significantly higher CH 4 concentrations, but the volume of water discharged is much lower and the overall amount of CH 4 outgassed is likely to be of the same order as the aquifer release. The generally low concentrations of CH 4 in groundwater supplies suggest no threat of explosion, although groundwater released by excavations remains a hazard.

Dinocyst stratigraphy and palynofacies studies used for refining a sequence stratigraphic model—uppermost Oligocene to lower Miocene, Jylland, Denmark

The uppermost Oligocene– Miocene deposits in the central and southern parts of Jylland, Denmark, comprise a complex succession of siliciclastic, paralic deposits. The coarse-grained parts of the succession comprise important groundwater reservoirs. A sequence stratigraphic model has gradually been developed during the last 7 years and the succession is now subdivided into six sequences (sequence A–F). The model is based on a combination of seismic data, geophysical logs and lithological data from boreholes and sedimentological measurements of outcrops. The present study documents the composition of assemblages of organic-walled dinoflagellates (dinocysts) in the lower part of the succession (sequences A–C). The data come from seven water supply boreholes and one outcrop section. The dinocyst data are an important tool for pointing out the sequence stratigraphic surfaces in the individual boreholes, showing distinct changes at the sequence boundaries and increased relative abundance and diversity of dinocysts at marine flooding surfaces. The dinocysts are also used for correlating between the studied boreholes and outcrops, for interpreting changes in the depositional environment and for dating the sequences in more detail than earlier datings based on molluscs and foraminifers. The datings allow correlation to eustatic sea-level curves. The good match between the sequence development and climatic changes suggests that eustatic sea-level changes were the main factor in sequence formation and changes in the depositional environment.

A note on the geochemical aspects of the Harrogate mineral waters

Three new water supply boreholes have been drilled in Harrogate and extend the available information on the hydrogeology of the mineral water springs. The water chemistry, combined with the geological evidence, shows that they tap waterat the opposite ends of the mineralized groundwater evolution system. Groundwater chemistry in the recharge area is available for the first time and there is new evidence that the deep migration of mineralized waters extends further than has been found hitherto. A conceptual model for the groundwater circulation system has been developed and a possible source of the high sodium chloride content is postulated.

Village water supply in Botswana: assessment of recommended yield for production boreholes in a semi-arid environment

More than 90% of the rural villages and settlements throughout Botswana have water supplies based on groundwater. The annual increase in water demand is about 0.3 × 10 6 m 3 and on average around 60 new boreholes are needed annually. In parallel with construction of new production boreholes for rural villages, there is an on-going rehabilitation of existing boreholes which have lost their original yield due to clogging, corrosion, encrustation, etc. The total annual cost of siting, drilling and testing of around 100 new production boreholes for rural villages water supply is estimated at around US$7.5 million (1997 price). Modelling of every groundwater resource for rural village water supply in Botswana is currently not feasible due to a lack of relevant and detailed information. A modelling exercise will assess the resource of the aquifer being studied, but can not give an assessment of the yield of each production borehole. Groundwater supply to rural villages is therefore currently based on the abstraction possible from established production boreholes. Test pumping data from these boreholes are the prime information in such an assessment. However safety factors and the fact that drought periods of longer duration are common in a semi-arid environment must also be considered. A computer program package TESTCURV developed by the Department of Water Affairs is a most useful tool in the assessment of yields for production boreholes for village water supply in Botswana, based on the performance of the well and the aquifer. No replenishment is assumed and the question of sustainable yield is not addressed by the program.

Groundwater pollution by chlorinated solvents: the landmark Cambridge Water Company case

Abstract The case of Cambridge Water Company v Eastern Counties Leather plc and v Hutchings and Harding Ltd is believed to be the first case this century in which common law principles have been applied to groundwater pollution in England. The case concerned the pollution of a public water supply borehole at Sawston, Cambridgeshire, by the chlorinated solvent tetrachloroethene, and the attempts by the water company to recover damages from the alleged polluters. Following discovery of the pollution in 1983 and subsequent investigations, the case was heard in the High Court in 1991, the Court of Appeal in 1992, and was finally decided by the House of Lords in 1993. This paper sets out the background and chronology of the case, reviews the investigations into the nature and extent of groundwater pollution, and then considers the legal arguments and findings of the courts and the House of Lords. The paper concludes with a discussion of some of the technical implications of this case, especially in relation to the collection of hydrogeological evidence.

Electrical Leak Detection System for Landfill Liners: A Case History

AbstractAs landfill specifications become more stringent in the United Kingdom, the development of increasingly sophisticated monitoring methods is necessary to meet environmental protection goals. This case history describes the development of a 2‐million‐cubic‐meter‐capacity landfill located in a sandstone quarry and 1 km from a public water supply borehole, where the sensitivity of the site to ground water contamination and the proximity to a public water supply borehole are particular issues.The landfill design incorporated a more sensitive environmental monitoring system, using a geophysical technique. The monitoring system comprises a permanent grid of electrodes installed beneath the landfill, connected by multicore cable to a computer‐controlled earth resistance meter and switching unit in the site weighbridge. It was designed to detect holes in the landfill liner prior to and after covering with waste and to monitor the migration of contaminants beneath the landfill before they reach the perimeter observation boreholes, should leakage occur.Such monitoring can enable the integrity of the landfill to be routinely reviewed; holes can be repaired if they are readily accessible and, if not, monitoring provides an early warning to enable the implementation of any additional monitoring or corrective action, based on the environmental risk posed by the site.The system was first used as a quality assurance test once the landfill liner, which covered an area of 3 hectares, was installed. The system proved sensitive, detecting a hole consisting of two narrow knife cuts. Such sensitivity allows a high degree of confidence to be placed upon the integrity of the liner resulting in a significant contribution to public reassurance. The landfill is now operational, and monitoring using the geophysical system will be undertaken on a monthly basis for the first year, with the frequency of monitoring reviewed thereafter.

Field observations of iron biofouling in water supply boreholes

Iron biofouling continues to be a significant cause of water supply borehole inefficiency and failure in the UK, yet there are still many misconceptions and a lack of understanding of the causes of iron biofouling. This is, in part, due to the lack of systematic research into this subject in the UK. This communication outlines key factors thought to cause the occurrence of iron biofouling in boreholes and suggests appropriate preventative measures based on field experiences. It is suggested that the degree of biofouling and its consequences depend upon the interaction of engineering and environmental factors and that prevention and control requires awareness of all such controlling influences.

Borehole siting in an African accelerated drought relief project

Abstract In response to recent droughts in central Africa, an accelerated well drilling programme was commissioned in Victoria Province, Zimbabwe. Geophysical techniques involved in the siting of 370 boreholes included electromagnetic profiling and resistivity sounding, the latter using the offset sounding system. An analysis of the field data showed that although observed errors were low, a significant proportion of the soundings were affected by strong lateral changes in resistivity, this probably indicating the presence of a very irregular bedrock surface. Nevertheless, mean regolith thickness and lithology were reliably estimated. Geomorphological features which were found to have the greatest potential for water supply boreholes include valleys and zones of weathering around bornhardts. In these situations geophysical surveys proved useful in locating areas of thickest regolith. Borehole yield could then be estimated from the measured formation resistivity although a precise relationship was somewhat masked by the clay mineralogy of the regolith and the type of bedrock which must be taken into account when siting boreholes.

An exploration strategy for higher-yield boreholes in the West African crystalline basement

Abstract In Burkina Faso investigations have been carried out to test satellite imagery and electromagnetic (EM) methods as a means of improving the siting of water supply boreholes in fissured rocks of the crystalline basement. The results show that these methods may be used to locate boreholes with above average groundwater yields, and to reduce the failure rates. Geometrical analysis of Landsat-MSS lineaments reveals the relevant regional fracture pattern, the present-day principal stress field and the resulting system of oriented hydraulic conductivities. Structural analysis of the lineament pattern and identification of dry-season-active vegetation on Landsat-TM imagery permit promising locations to be pinpointed for groundwater abstraction. EM-measurements on a two-dimensional grid using the ‘very low frequency’ (VLF) and ‘horizontal loop EM’ (HLEM) methods are used to locate potential fractures on a local scale as a basis for rational borehole siting. The methods, applied separately or in combination, offer an economical approach for use in rural and community water supply, small-scale irrigation and water resources planning. The methods appear to be generally transferable to fissured hard rock aquifers in other regions. The best suited settings are believed to be on cratons and platforms in a semi-arid climate.

The use of ground electrical survey methods for siting water-supply boreholes in shallow crystalline basement terrains

Abstract Resistivity methods are widely used as an aid to siting water-supply boreholes in basement terrain. Adverse conditions due to shallow bedrock can be identified readily but specific targets such as narrow conductive zones may be missed; quantitative interpretation may be less reliable than is often assumed. Electromagnetic (EM) profiling will detect localized zones of deeper weathering and the effects of fracturing at shallow depths, and it is used for the precise location of anomalous ground indicated by lineations on aerial photography. Routine EM surveys give better lateral resolution than resistivity for the conductive targets of interest. The 2-D and 3-D EM modelling techniques needed for interpreting the conductor geometry realistically are still under development. Geophysical methods must be applied with due regard for the targets being sought and the local geological setting: they will not always be appropriate and resources should be targeted on districts where problems can be solved. Qualitative interpretations are adequate in some situations but more rigorous field procedures and analytical techniques are needed to ensure that useful hydrogeological information is obtained.

Locating the Sherwood Sandstone aquifer with the aid of resistivity surveying in the Vale of York

Abstract The Sherwood Sandstone aquifer in the Vale of York is generally confined beneath thick clay drift in the west and by thin drift plus an increasing thickness of Mercia Mudstone towards the east. Published geological maps show a gentle easterly dipping succession cut by one major east-west fault passing through Stamford Bridge. The junction between the Sherwood Sandstone and the Mercia Mudstone is shown by a north-south trending line south of this fault. Recent boreholes for water supply have shown that the structure is more complex however, and reliable predictions of depths to the aquifer frequently cannot be made without pre-drilling surveys. Consequently the results of over 50 resistivity sounding have been used in conjunction with all available well logs to redraw the important hydrogeological boundary between the Sherwood Sandstone and the Mercia Mudstone across the central part of the Vale. The results have shown that depths to the aquifer, up to around 200 m, can generally be predicted prior to drilling to within 100y surface resistivity methods, except where the ‘Mudstone’ is very thin in the ‘feather-edge’ zone. The results have also shown the presence of many persistent east-west or northeast trending faults with vertical throws up to 80 m and some strike faults or monoclines in this part of the Vale. The significance of these faults to groundwater flow and water extraction are discussed. Wireline logs at six wells suggest the occurrence of at least two thick units of gypsum and anhydrite within the Mercia Mudstone. These cause high, 100-150 ohm m, depth averaged resistivity values to be computed for the Mercia Mudstone.

Diagnosis and monitoring of biofouling in enclosed flow systems — experience in groundwater systems

A monitoring cell (moncell) has been developed for the diagnosis and monitoring of biofouling and other problematic processes in groundwater systems. The device, relatively simple in design and application, is proving to be a useful tool, particularly for engineers who are not always aware of the processes occurring within their systems. All too often the yields from water supply boreholes and irrigation tubewells can decline without initially causing due concern. Yield decline can result from the clogging of parts of the system, (e.g. the screen, filter, pump, pipework) due to biofilm growth, chemical/biochemical deposition, and/or particle migration. Being unaware of the problem, or the nature of the problem, for too long a period can often lead to complete failure of the system. Early diagnosis is essential for optimum operation, maintenance and if necessary rehabilitation of the system. Trials with the moncell suggest that it could be used in other enclosed flow systems where a simple visual monitorin...

The diagnosis of seventy municipal water supply boreholes in Lima, Peru

Borehole diagnoses were carried out in the wake of declining yields and falling water table in the Lima aquifer. The objective was to evaluate, from a representative sample, the rehabilitation that would be required to restore yields and supply increasing demands. Rehabilitation methods are well described in literature. However, the selection and evaluation of techniques, appropriate in a given hydrogeological context, are not well known. This paper describes the current status of the Lima aquifer and the investigations performed in selecting appropriate rehabilitation. It is a case history of comprehensive diagnosis in 70 boreholes. Seven items of field tests were carried out on each borehole, including pumping tests, downhole closed-circuit TV (CCTV) survey, detailed hydrochemical analyses and pump inspection. Rehabilitation needs were evaluated from standardized analyses of hydrogeological and electrical-mechanical data. An effective plan for ongoing rehabilitation, formulated to sustain future supplies was based on the diagnosis. Rehabilitation, aimed at reducing well losses, increasing the length of water column in the borehole and improving the operating efficiency of pumps are the main recommendations of diagnosis. Yield improvement by 56% and increase of the useful life of boreholes by 10 years has been projected from the diagnosis. The programme of rehabilitation is to be implemented.

Locating potential borehole sites in a discordant flow regime in the Chalk aquifer at Lulworth using integrated geophysical surveys

Summary Groundwater flow in the Chalk Aquifer at Lulworth is discordant with the surface drainage pattern as a result of flow reversal consequent upon coastal breaching of the aquifer. Siting of boreholes for water supply is thus made difficult, especially since flow is confined to very narrow zones. The use of geophysical techniques has enabled such zones to be identified with varying degrees of certainty. It is important not to place too much reliance on a single technique and to integrate such surveys into an overall appreciation of the evolution of the groundwater flow regime in order to obtain maximum benefits.