Coliform bacteria and nitrate contamination of wells in major soils of Frederick, Maryland

An investigation was conducted on the hypothesis that inadequate system construction or placement may cause contamination of wells with coliform bacteria and/or nitrates. Specifically, two predictions were tested: 1. A negative correlation between lot size and coliform bacteria and nitrate contamination will exist in unsewered areas. 2. Coliform bacteria and nitrate contamination will decrease with increasing casing length. The relationship of coliform bacteria and nitrate levels to lot size and casing length was tested for all wells in unsewered areas (n = 832) and for wells in 10 soil groups in Frederick County, Maryland, to determine if septic system construction or placement contributed to well contamination. Coliform bacteria and nitrate contamination were negatively correlated with lot size. In addition, coliform bacteria levels were negatively correlated with casing length, and there was a trend toward nitrate levels being associated with casing length. The results suggest that septic systems may be a source of coliform bacteria and nitrate contamination of wells. The casing length required in well construction should be increased in areas where wells may be prone to coliform bacteria contamination if the minimum amount of casing is used.