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Agriculture and Nitrate Concentrations in Maryland Community Water System Wells

Dep. of Agricultural and Resource Economics, Univ. of Maryland, College Park, MD 20742-5535

Lisa K. Shapiro

Gallagher, Callahan, and Gartrell, 214 North Main Street, Concord, NH 03301

^* Corresponding author (erikl{at}arec.umd.edu).

ABSTRACT

The presence of NO₃-N in well water is a cause of growing concern throughout the USA. Previous studies indicate that agriculture is a major contributor to this problem. This study uses data on NO₃-N concentrations in drinking water wells, on hydrological characteristics of those wells, and on measures of agricultural activity and of the extent of residential land use to construct statistical relationships between land use and well water quality in Maryland community water system wells. Tobit regression was used to correct for truncation bias arising from the fact that NO₃-N was not reported at concentrations below 0.1 mg/L. Exponential and linear specifications were estimated; non-nested hypothesis tests indicated that the exponential specification fit the data better than the linear one. Deeper wells appear less vulnerable to NO₃-N contamination, wells in unconfined aquifers and especially limestone formations, more so. Broiler and corn (Zea mays L.) production were associated with higher NO₃-N concentrations in drinking water in both specifications, indicating that agriculture-oriented efforts aimed at preserving groundwater quality should be concentrated on corn and broiler production. Septic systems for waste disposal also appear to have a substantial impact on NO₃-N concentrations in drinking water, suggesting that land use planning measures such as minimum lot size zoning may be needed to prevent conversion of crop and livestock production to residential units relying on septic systems from exacerbating groundwater quality problems.

Scientific Article no. A-7892, Contribution no. 9226 of the Maryland Agricultural Experiment Station.

This research was supported in part by the Economic Research Service, .U.S. Department of Agriculture, under Cooperative Agreement 58-3AEM-8-00065 and by the Maryland Agricultural Experiment Station Competitive Grants Program.

Received for publication January 12, 1996.