but when groundwater impacts occur, they are relatively more difficult to identify and mitigate. Polluted groundwater undergoes some natural purification as it percolates through soil columns prior to reaching the water table. However, due to the relatively low flow rates associated with groundwater, pollutant removal and dilution are often retarded, and groundwater pollution therefore can remain a localized problem for significant lengths of time. As such, there could be a substantial time interval before groundwater pollution can be observed (Morris and Therivel, 2001