Abstract:
Carbonate aquifers provide important sources of potable water but are known to be particularly prone to pollution owing to rapid transfer of pollutants from the surface to springs or boreholes. Source protection zones and groundwater vulnerability maps are commonly used to mitigate against the pollution hazard but cannot be applied simplistically to carbonate aquifers, which are usually highly heterogeneous with overlapping groundwater divides that may vary with water levels. Divergent flow and disjunct contributory areas provide further complexity. Under these conditions, water-tracing experiments, repeated under different flow conditions, are the only tool capable of identifying those areas that contribute recharge to a particular source. Examples of water pollution affecting disjunct and overlapping source contributory areas are presented from the Waitomo area (New Zealand), Cuilcagh Mountain (Ireland) and the Peak District (UK). Source protection zones (SPZ), that have been defined by the Environment Agency in the Buxton area of the Peak District using equivalent porous medium models, are shown to be deficient. Further water-tracing experiments are essential if carbonate aquifers are to be adequately protected from pollution