Drinking waters pumped from shallow glacial-fluvial aquifers are being contaminated with fecal coliform bacteria and it is likely that nearby polluted surface waters are the source of this contamination.
Bacteria are the most common pathogenic contaminants.
Due to downward hydraulic gradients induced by pumping, contaminated surface water may be drawn into the underlying aquifer and move towards drinking-water wells. Under US EPA guidelines, wells less than 50 ft from surface water are considered under the direct influence of surface water. Upgrading typical groundwater treatment to include these techniques can be quite costly and in many circumstances prohibitive, resulting in wel l abandonment and the costly search for new water supplies. The studies cited above suggest that the 50-ft criterion will not be cautious enough in some settings. Adequate guidelines for appropriate separation distances need developing and should be based on our best ability to predict bacterial transport in a variety of hydrogeologic settings.