COLIFORM BACTERIA AND NITRATE CONTAMINATION OF WELLS IN MAJOR SOILS OF FREDERICK, MARYLAND

An investigation was conducted on the hypothesis that inadequate syste m construction or placement may cause contamination of wells with coli form bacteria and/or nitrates. Specifically, two predictions were test ed: 1. A negative correlation between lot size and coliform bacteria a nd nitrate contamination will exist in unsewered areas. 2. Coliform ba cteria and nitrate contamination will decrease with increasing casing length. The relationship of coliform bacteria and nitrate levels to lo t 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 wer e 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 r esults suggest that septic systems may be a source of coliform bacteri a and nitrate contamination of wells. The casing length required in we ll construction should be increased in areas where wells may be prone to coliform bacteria contamination if the minimum amount of casing is used.