Groundwater development techniques
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What does groundwater development involve?
Developing groundwater for water supply can involve various different activities, depending on the hydrogeological environment, how much groundwater is needed and what it will be used for. It is usually also important to develop groundwater sources sustainably, so that the groundwater resource is protected and maintained for future supplies.
At its simplest, groundwater flowing naturally from a spring can be directly tapped with very little effort, although protecting that spring, so that the water doesn't become polluted, can be more difficult. In another simple example, where groundwater levels are shallow and the aquifer is easy to dig through (e.g. sand or gravel), hand dug wells can be quite easily constructed to allow groundwater to be abstracted - but again, protecting the groundwater in the well from pollution can be more difficult.
Where the aquifer and/or groundwater levels are deeper, or the aquifer can't be easily dug through by hand, developing groundwater resources is more complicated. It is likely to need some kind of mechanical drilling - either manual drilling, or using a drilling rig.
In areas where the aquifers are all permeable and productive, water boreholes can often be drilled just about anywhere. But in areas with low permeability and/or complex aquifers, or where there are groundwater quality issues, new boreholes and wells must be sited and designed carefully if they are to be successful. To do this, it's important to understand how groundwater exists and behaves in the area.
Stages in a groundwater exploration programme
The main stages of a groundwater exploration programme - which will allow you to assess and sustainably develop groundwater resources - are summarised in the table below, with an indication of costs. Some more detail on each stage is given in the sections below, but this page is not a comprehensive guide to groundwater development. Many other resources are available which do provide detailed guidance and support for groundwater exploration and development, and some of these are listed at the bottom of this page, under Links to more information.
|Stage||Notes on costs|
|Siting Boreholes or Wells|
|Reconnaissance: gathering maps and information (e.g. from existing reports, academic papers etc) on geological and hydrogeological conditions. This is an essential first step for understanding groundwater resources.||A one-off cost: several weeks time of a project staff member or consultant. If new data have to be bought or generated (e.g. from satellite images or field mapping), costs will increase, but not prohibitively so.|
|Hydrogeological fieldwork: making field observations of the local geology (e.g. from rock exposures or chippings/cuttings from any local hand-dug wells or previously drilled boreholes); hydrogeology; and existing water sources (both dry and wet season sources), and gathering relevant information from discussions with the local community: e.g. how much do existing sources yield; do yields fall or dry up in the dry season; are there water quality problems? Also observe any local pollution sources, such as pit latrines, burial grounds, cattle pens or market areas. This should be done by someone experienced (e.g. who has developed boreholes in this area, or similar areas, before).||Requires a well-trained engineer or hydrogeologist to visit the area.|
|Geophysical surveying: e.g. resistivity or electromagnetic (EM) techniques. Must be combined with reconnaissance data and hydrogeological fieldwork. It is important to analyse geophysical data correctly so that it gives good information. Investment in training staff is often beneficial.||Geophysical equipment varies in price, but for a single technique (eg resistivity) is generally less than $US20 000. A well-trained geophysics team will need to spend at least 1 day in each area targetted for a new borehole.|
|Collecting information during drilling: gathering information on geology (e.g. from logging drilled rock chips and measuring penetration rates) and hydrogeology (e.g. from water strikes). Borehole drilling is a unique opportunity to collect useful geological and hydrogeological data from deep underground - data that are not otherwise available.||A well-trained hydrogeologist or engineer should be onsite during drilling to supervise the drilling and collect good data.|
|Assessing source yield: in most cases, this means assessing the sustainable yield of a borehole or well by carrying out a pumping test. For springs, it may mean measuring spring flow in different seasons. It is important to measure how much the source will yield sustainably in order to know how many people it can serve.||A well-trained hydrogeologist or engineer is needed to carry out a pumping test, and normally they need at least 1 day per borehole. For higher yielding boreholes, an electric pump and generator are likely to be needed.|
|Assessing water quality: measuring the most important chemical and biological parameters that can impact human health.||Some parameters can be measured quickly in the field using relatively simple equipment, but most need to be collected and sent to a laboratory. A well-trained field technician may be needed to carry out sampling.|
Types of groundwater sources
Groundwater can be abstracted from the ground in different ways. Many resources are available to support the choice of which abstraction method to use in different environments - there are some references at the bottom of this page.
Groundwater is most often accessed through springs, hand-dug wells, or drilled boreholes. (Drilled boreholes are also sometimes called wells!).
- Springs are natural flows of groundwater from the underlying rock or unconsolidated sediment. Springs are dependent on the characteristics of the rocks, and their nature and yields are hugely variable. They often occur in specific hydrogeological environments. Because they are open at their source, springs are vulnerable to contamination. No equipment is needed to make a spring, but springs can be improved and made less vulnerable to contamination and drought by various developments, such as constructing a collection tank to store spring water, and installing a protective cover over the spring head.
- Hand-dug wells have been dug to access groundwater for thousands of years. They can only be dug in soft material, such as unconsolidated sediment like sand and gravel, weathered basement, or limestone. They are only appropriate where the groundwater level (water table) is shallow. They are usually less than 20 m deep and 1–2 m in diameter, but can be wider and much deeper. Little or no specialised equipment is needed to construct a well – just something to dig with, and a way of removing the spoil. Wells often need to be lined to keep them open, using materials like brick, stones, concrete rings or even lorry tyres. Open wells are vulnerable to contamination from the surface, and can be improved by installing a concrete apron around the top. Wells have large storage, which helps make them less vulnerable to drought, but because they typically tap only shallow groundwater, they can dry up in dry seasons or longer droughts.
- Boreholes are narrow diameter tubes drilled into the ground, usually vertically. Boreholes are also called tube wells or simply wells. They can be drilled more quickly and go deeper than hand-dug wells, and so can tap deeper, often more sustainable groundwater; they can be drilled though hard rocks and they can be more easily protected from contamination. There are many different techniques for drilling boreholes, some of which are more suited to certain hydrogeological environments. Usually, a motorised drilling rig is used, operated by specialist drillers. There are also manual drilling techniques.
Other, less common ways of accessing groundwater are by:
- Collector wells, which are vertical boreholes or wells modified by drilling horizontally out radially below the water table to increase the collection area for groundwater into the central well, from where water is abstracted. They are often constructed in alluvium, next to ephemerally dry ('sand') rivers, with the horizontal radials drilled into the river bed deposits; or in weathered basement.
- Infiltration gallery, which is a horizontal trench or drain dug below the water table to abstract shallow groundwater, usually from unconsolidated alluvium, including sand rivers, or windblown deposits. The trench drains into a sump from where water is abstracted. The gallery may have to be lined to keep it open.
- Qanats, which are an ancient method of tapping and transporting groundwater in many parts of North African and the Middle East. A qanat comprises a mother well, often in alluvial deposits at the edge of a mountain range, and a gently inclined covered, underground channel which allows groundwater to flow downhill to a village.
Testing the yield of a groundwater source
There are different ways of testing the yield of a borehole or well to assess how much it can sustainably provide, but they all involve measuring the maximum pumping rate that can be sustained for a reasonable drawdown of the water level (i.e., so that the water level stays above the pump intake). The following is a brief summary, and more detail is available in MacDonald et al. (2001) and MacDonald et al. (2005).
An initial estimate of borehole yield can be made when the borehole is airlifted after drilling, but this is a very approximate method. It gives no information about water level drawdown in the borehole, and therefore no information about the sustainable yield. However, it can indicate whether a borehole is likely to be productive enough to be worthwhile installing screen and casing, and what size of pump to use for a pumping test.
A short, simple pumping test that is suitable for a relatively low yielding borehole capable of supplying enough water for a hand pump for 250 people, is a bailer test. Water is removed from the borehole with a bailer of known volume for a short time – e.g. 10 minutes – and the water level is measured as it recovers, usually for about 30 to 60 minutes. The equipment needed is a 20 m rope; a stopwatch; a water level dipper; and one or preferably two simple bailers that will fit freely down the borehole. The results can be analysed using sound theoretical principles. The procedure for carrying out and analysing a bailer test is given in MacDonald et al. (2001).
For higher yielding boreholes, a constant rate test using an electrical pump should be carried out. This involves pumping the borehole at a constant rate for a certain period – usually at least 3 hours – and measuring the change in water level in the borehole during pumping and after pumping stops, as the water level recovers. The test results are analysed to give information about aquifer transmissivity – a measure of how easily groundwater can flow through the aquifer. A constant rate test requires a water level dipper and stopwatch, and an electrical pump of suitable size to match the potential borehole yield. A procedure for carrying out and analysing a constant rate test is given in MacDonald et al. (2001).
Groundwater can be abstracted from boreholes and hand-dug wells by traditional methods (buckets, etc), by hand pumps, or by mechanical (e.g. diesel) or electrical submersible pump. Mechanical or electrical pumps are most appropriate for higher yielding wells or boreholes. Most rural water supply boreholes and wells in Africa are installed with hand pumps. There are many different types of hand pump, and the choice of which to use will depend on national standards, ease of maintenance and local expertise, availability of spare parts, the depth of water lift required, the groundwater chemistry (mild steel can corrode), and cost. RWSN provides many resources on hand pumps, including technical manuals and a number of discussion documents on practice and policy.
Assessing groundwater quality
The quality of groundwater is almost as important as the yield of a source. In most cases, groundwater from a properly constructed borehole is of good quality and suitable for drinking without any treatment, but some natural elements and pollutants can make groundwater smell or taste unacceptable, or even make it harmful to health. Testing the chemical and bacteriological quality of groundwater is therefore always a good idea. The World Health Organisation sets guidelines for drinking water quality. A brief introduction to groundwater quality issues and measurement can be found in MacDonald et al. (2001). Some more background on groundwater quality, particularly related to Africa, is in the Groundwater quality resource page.
Links to more information
Danert, K. 2015. Manual Drilling Compendium 2015. RWSN Publication 2015-2, Skat, St Gallen, Switzerland.
Danert, K. 2015. Chad’s Growing Manual Drilling Industry. , Skat Foundation, St Gallen, Switzerland.
MacDonald, A M, Davies, J, and Ó Dochartaigh, B É. 2001. Simple methods for assessing groundwater resources in low permeability areas of Africa. British Geological Survey Commissioned Report, CR/01/168N.
MacDonald, A M, Davies, J, Calow, R, and Chilton, J. 2005. Developing groundwater: a guide for rural water supply. ITDG Publishing, NERC 2005. This book is a comprehensive manual for how to develop groundwater for rural water supply, based on extensive experience in Africa. Each chapter of the book can be freely downloaded from the Practical Action Publishing website.
MacDonald, A M, and Calow, R C. 2009. Developing groundwater for secure rural water supplies in Africa. Desalination, 248 (1-3), 546-556. doi: 10.1016/j.desal.2008.05.100
World Health Organisation. 2011. Guidelines for drinking-water quality, 4th edition. ISBN: 978 92 4 154815 1