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.
Private wells are also susceptible to bacterial contamination.
Counterintuitively, there was an invers e relationship with distance from feedlots or septic systems and testing positive for total coliform bacteria. Clearly, both rural populations obtaining drinking water from private wells and municipal populations obtaining drinking water from aquifers adj acent to polluted surface waters are at risk of waterborne disease. Once allochthonous bacterial tra nsport through groundwater aquifers is better understood, greater protection of groundwater to be used as drinking-water sources will be possible. To meet our objective we will conduct laboratory experiments on the transport of allochthonous bacteria thro ugh groundwater sediments. Using these results, we will then construct a predictive model that balances utility with efficacy by including only necessary physical, chemical and biological parameters.