Author: Bruce Misstear, Associate Professor, School of Engineering, Trinity College Dublin and Vice President, International Association of Hydrogeologists
About four billion people get their water supply from a groundwater source and groundwater underpins much of the world’s food production (through irrigation), yet there is still a lack of awareness about this important resource.
In Ireland, people often regard groundwater as a somewhat mysterious substance, as illustrated by the large number of holy wells here (perhaps around 3,000) and the (still) widespread practice of using water diviners for locating new sources. Whereas most of our cities obtain their water supplies from a river, lake or reservoir, groundwater is the main source of drinking water in rural areas. Unusually for such a small country, we have a very large number of private wells – in excess of 150,000, most of which are boreholes. A properly sited and constructed borehole can provide a safe and reliable water supply. However, in reality, many of our private wells are poorly located, being close to pollution sources such as septic tank systems or farmyards, or are poorly constructed1.
[caption id="attachment_8810" align="alignright" width="928"] Fig 1. A key requirement in the design of a well is installing a cement grout seal behind the water well casing to prevent ingress of surface pollutants ('Water Well Guidelines', Institute of Geologists of Ireland, 2007) (click to enlarge)[/caption]
Figure 1 shows an example of a good well design, one that includes a sanitary seal between the borehole lining and the drilled hole. Many private wells, however, do not have such a sanitary seal and therefore are susceptible to pollutants finding a relatively rapid pathway from the land surface to the well intake via the space behind the borehole lining.
A recent research project found that there was a lack of awareness amongst private well users in Ireland of whether or not their well contained such a sanitary seal (only 22 per cent awareness)2 – this is a case where better education of consumers would help in ensuring better water quality in private well supplies and thereby reduce risks to public health from waterborne infections. National monitoring data for the period 2007-2009 showed that about a third of samples from the groundwater monitoring network showed evidence of contamination by faecal coliforms, indicating the likely scale of the pollution problem3.
There are about 800 million people worldwide who do not have access to a safe water source. To rectify this situation, the majority of these people will have to be supplied in future from a groundwater source, in many cases through the construction of a shallow hand-dug well. Here, again, the hand-dug well must be protected against pollution by including a concrete lining and cover5.
[caption id="attachment_8812" align="alignright" width="380"] Fig 2. A hand-dug well in Uganda with a concrete apron and drainage channel; this is a low-yielding well, as evidenced by the queue of water containers waiting to be filled (Photo: Bruce Misstear)[/caption]
Many of the wells in developing countries fail through the lack of adequate maintenance of the well and especially the hand pump. Sustainability is not just a matter of applying good engineering practice, but also depends on other important issues including governance, finance, sociology and health. All of these issues are being addressed in an integrated research project called Water is Life in Uganda (Fig. 2). This Irish Aid and Higher Education Authority-funded project involves several Irish third-level institutions plus Makerere University in Uganda and an Irish NGO. One of the research themes is sustainable groundwater supplies, including the impacts of future climate change on water levels and water quality.
[caption id="attachment_8962" align="alignright" width="1503"] Fig 3. Schematic showing pollution pathways via a fractured bedrock aquifer to a river (Source: WFD Visual)[/caption]
In addition to being an important source of drinking water, groundwater helps to keep our rivers flowing, especially in dry summers, and sustains many of our most important wetland habitats. If groundwater gets polluted, then these pollutants may end up in rivers in lakes.
Understanding the pathways by which pollutants such as nitrate and phosphate reach our surface waters is key to identifying the source areas for these pollutants. And if we know the source areas and origins of the pollution, then we can then try and manage the problem. This understanding of pollution pathways in Ireland is central to an ongoing research project sponsored by the Environmental Protection Agency6,7 (Fig. 3 and also main image, above).
In conclusion, groundwater plays a vital role in our water supply and in our environment. Greater awareness of this precious resource is necessary to ensure its proper management and protection.
Bruce Misstear is Associate Professor at the School of Engineering, Trinity College Dublin and is Vice President of the International Association of Hydrogeologists.
1Hynds P, Misstear B & Gill L (2012) Development of a microbial contamination susceptibility model for private domestic groundwater sources. Water Resources Research, doi:10.1029/2012WR012492, 2012
2Hynds P, Misstear B & Gill L (2013) Unregulated private wells in the Republic of Ireland: Consumer awareness, source susceptibility and protective actions. Journal of Environmental Management, 127: 278-288
3Environmental Protection Agency (EPA) (2010), Water quality in Ireland 2007–2009. EPA Wexford
4Institute of Geologists of Ireland (2007). Water well guidelines
5Misstear B, Banks D & Clark L (2006) Water wells and boreholes. J Wiley & Sons
6Archbold M et al. (2010) Contaminant movement and attenuation along pathways from the land surface to aquatic receptors – a review, STRIVE Report Nr 56, Environmental Protection Agency, Wexford
7O’Brien R, Misstear BD, Gill LW, Deakin J & Flynn R (2013) Developing an integrated hydrograph separation and lumped modelling approach to quantifying hydrological pathways in Irish river catchments, Journal of Hydrology, 486: 259-270