EFFECTS OF URBAN LAND USE ON SHALLOW GROUND-WATER QUALITY IN STRATIFIED-DRIFT AQUIFERS - COMPARIOSN OF DATA FROM THE HUDSON RIVER BASIN, NEW YORK, AND THE CONNECTICUT RIVER BASIN, CONNECTICUT AND MASSACHUSETTS.

Comparison of concentrations of nitrate and select man-made organic compounds in water samples collected from 25 wells in the Hudson River basin, New York, and 13 wells from the Connecticut River basin, Connecticut and Massachusetts, indicate that regional differences in shallow ground-water chemistry exist in urban areas for some organic constituents. The urban study areas, consisting of mixed residential and commercial land-use, overlie unconsolidated sand and gravel (stratified-drift) aquifers derived from calcareous- clastic and metaclastic or siliceous crystalline bedrock. Wells sampled are generally shallow; well depths in the Hudson River study area range from 3 to 21.5 meters below land-surface with a median of 6.3 meters, and well depths in the Connecticut study area range from 3.5 to 8.5 meters with a median of 5.5 meters.

Concentrations of nitrate in the Hudson River study area range from less than the reporting limit of 0.05 milligrams per liter (mg/L) to 17 mg/L, with a median of 0.3 mg/L; nitrate concentrations from the Connecticut study range from 0.05 mg/L to 9.7 mg/L, with a median of 2.35 mg/L. The median nitrate concentrations are not significantly different. The elevated concentrations of nitrate in both data sets show some effect of urban land-use practices on shallow ground-water quality. Sources of nitrate in urban areas include septic systems, leaky sanitary sewers, and fertilizer applications to lawns.

Chloroform, detected in 28 percent of the wells, was the most frequently detected volatile organic compound. Chloroform concentrations ranged from 0.3 to 0.6 micrograms per liter (ug/L) in the Hudson River study area, and from 0.2 to 1.3 ug/L in the Connecticut River study. The widespread occurrence of chloroform beneath urban areas could result in part from chlorination of natural and man-made organic compounds by chlorinated water supply and wastewaters. No pesticides were detected in the Hudson River study area. Trace concentrations of six pesticides, mainly herbicides, were detected in 54 percent of the samples from the Connecticut study. Prometon, a wide-spectrum herbicide was detected at concentrations of 0.01 to 0.06 ug/L in more than 30 percent of the Connecticut study urban wells. Differences in detections of volatile organic compounds and pesticides could reflect differences in specific land-use practices or in well-depth.

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