Nitrate contamination in private wells in rural Alabama, United States

Nitrate-N (NO3−-N) concentrations in random water samples from rural residential wells in Alabama, USA, were analyzed over an 8-year period from 1992 to 1999. Data collected included land use, well depth, septic tank use and distance from the well and also livestock and cropping activities around wells. Of 1021 available data sets, 36% of samples showed nitrate-N concentration of higher than 1.0 mg/l, indicating the possible influence of anthropogenic activities. About 1.7% of samples had a nitrate-N concentration of higher than 10 mg/l. Results indicate nitrate contamination in groundwater was relatively low and stable in Alabama. Logistic regression analysis indicated that well depth, pH, and cropping activity were factors of statistical significance in influencing nitrate-N concentration in these wells. Factors such as septic tank use and livestock activities did not show a close link to nitrate-N concentration in wells tested.