Groundwater systems

Groundwater is a vulnerable resource. As schemes are developed to pump out huge quantities of water, and with the advent of particularly persistent contaminants, the resource needs to be protected and managed (see Table 2.1). Despite groundwater’s pivotal role in sustaining ecosystems and providing water supply, the resource is still poorly understood, and hence poorly managed, in many parts of the world. When things go wrong, the damage can be lasting or even permanent. For example, over-pumping and continuous long-term contamination by urban effluents and agricultural practices in the Gaza Strip has led to some groundwater becoming unfit for drinking or agricultural use. Even if pumping and contamination stopped today, it would take hundreds of years for the contaminants and intruding saline water to be flushed out of the groundwater system. Some groundwater resources were accumulated aeons ago and are no longer replenished (e.g. many of the sandstone aquifers of North Africa), thus using them is similar to mining non-renewable minerals

Global change and groundwater

Groundwater (contained in sediments and rocks) constitutes the planet’s predominant reserve of fresh water, commonly with storage times from decades to centuries and millennia. Groundwater resources thus provide an excellent ‘buffer’ against the effects of climate variability on surface-water supplies, because of the generally large and widely- distributed storage reserves of aquifer systems. But questions arise as to how naturally resilient are groundwater reserves themselves to global change, and whether we are doing enough to help conserve and protect them

Assessing and controlling the impacts of agriculture on groundwater : from Barley Barons to Beef Bans

One of the less obvious, but most insidious, effects of the enormous changes in English agriculture over the past 50 years has been the contamination of groundwater—originally by nutrients, subsequently by pesticide residues, and most recently by the livestock parasite Cryptosporidium. The paper analyses scientific understanding of the factors determining the origin, transport and attenuation of these contaminants in groundwater systems. It focuses primarily on the British situation, but draws on experience from Europe and beyond as appropriate. Given the essentially diffuse character of the mainly agricultural activity generating the subsurface contaminant load, pollution control has (presented (and continues to present) a complex regulatory challenge in legal, technical, economic and social terms. The discussion explores this challenge, which yet again has become very topical at national and European policy levels

Groundwater resources : balancing perspectives on key issues affecting supply and demand

Sustainable groundwater management requires (a) maximizing the use of aquifer storage to reduce water-supply costs while limiting environmental impacts, and (b) maximizing groundwater protection to reduce water-supply treatment needs while not unduly restricting land-use activities. These key issues are evaluated from the experience of a recent and comprehensive national strategic study, involving detailed consultation with many stakeholders with an interest in groundwater resources. Such balances are not easy to achieve because groundwater systems are complex to analyse and slow to respond to change, resulting in considerable uncertainty in assessment and prediction without in-depth research and high-resolution monitoring. Current institutional and regulatory arrangements for the water sector in England and Wales do not appear to be achieving the best possible use of aquifer storage and optimal investment in groundwater protection

Hydrogeological characterisation and water-supply potential of basement aquifers in tropical Africa

AbstractCrystalline basement rocks, with a mantle of weathered alternation products, occur beneath very extensive areas of tropical Africa. Low-productivity aquifers are widely, but rather unpredictably, present in this formation. They yield small water supplies vital to the rural population for domestic purposes and for livestock watering. On a more localised basis, a potential may exist to develop larger supplies that are adequate for small towns or for small-scale irrigation. This paper reviews advances in the understanding of this extensive hydrogeological system, resulting from British research and experience since 1980

Cryptosporidium contamination hazard assessment and risk management for British groundwater sources

Contamination of aquifers by Cryptosporidium oocysts has only recently been recognised as a risk to the security of important groundwater-based drinking water supplies in the UK. The predominance of dual porosity aquifers with complex flow systems, the fact that UK water utilities hardly ever own or control the catchments overlying the aquifer supplying their abstractions and the diverse designs of the wells/springs themselves renders hazard assessment necessary but not simple. A tripartite approach is proposed which is a modification of standard contaminant transport sourcepathwayreceptor principles. The complex interaction of factors and uncertainty of underpinning data greatly limit the applicability of a strictly numerical approach to risk assessment. Instead the importance is emphasised of understanding the blend of hydrogeological and operational factors which makes each site and its setting unique

The pollution threat from agricultural pesticides and industrial solvents A comparative review in relation to British aquifers

SIGLEAvailable from British Library Document Supply Centre- DSC:4344.4(BGS-HR--87/2) / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Assessing herbicide concentrations in the saturated and unsaturated zone of a Chalk Aquifer in Southern England

The behavior of the herbicides isoproturon (IPU) and chlortoluron (CTU) in ground water and shallow unsaturated zone sediments were evaluated at a site situated on the Chalk in southern England. Concentrations of IPU in ground water samples varied from <0.05 to 0.23 μg/L over a five-year period of monitoring, and were found to correlate with application of the pesticide. Concentrations of pesticides in ground water samples collected during periods of rising water table were significantly higher than pumped samples and suggest that rapidly infiltrating recharge water contains higher herbicide concentrations than the native ground water. Significant variations in herbicide concentrations were observed over a three-month period in ground water samples collected by an automated system, with concentrations of IPU ranging from 0.1 to 0.5 μg/L, and concentrations of a recent application of CTU ranging from 0.2 to 0.8 μg/L. Different extraction methods were used to assess pore water concentrations of herbicides in the unsaturated zone, and samples were analyzed by standard HPLC analysis and immunoassay (ELISA) methods. These data indicated highly variable concentrations of herbicide ranging from 4 to 200 g/ha for HPLC and 0.01 to 0.04 g/ha for ELISA, but indicate a general pattern of decreasing concentrations with depth. The results of this study indicate that transport of IPU and CTU through the unsaturated zone to shallow ground water occurs and that this transport Increases immediately following herbicide application. Measured concentrations of herbicides are generally lower than specified by the European Union Drinking Water Directive, but are observed to spike above this limit. These results imply that, while delivery of pesticides to ground water can occur as a result of normal agricultural practices, the Impact on potable supplies Is likely to be negligible due to the potential for degradation during the relatively long travel time through the unsaturated zone and high degree of dilution that occurs within the aquifer. As a result of the wide variation in concentrations detected by different techniques, it is suggested that for future site Investigations more than one sampling strategy be employed to characterize the occurrence of pesticide residues and elucidate the transport mechanisms