Relation between land use and ground-water quality in the upper glacial aquifer in Nassau and Suffolk Counties, Long Island, New York

The chemical quality of groundwater in the upper glacial (water-table) aquifer beneath the 10 types of land-use areas of Nassau and Suffolk Counties, NY was examined to evaluate the effect of human activities on groundwater. The highest median chloride and total dissolved-solids concentrations were found in wells in high-density residential areas (more than five dwellings/acre), and the highest median nitrate, sulfate, and calcium concentrations were found in wells in agricultural and high density residential areas. Relatively low median concentrations of inorganic chemical constituents were found in wells in undeveloped and low-density residential areas (1 or fewer/acre): volatile organic compounds were rarely detected in these same areas. The highest concentrations and most frequent detection of volatile organic compounds were in industrial and commercial areas. The most commonly detected volatile organic compounds were 1,1,1-trichloroethane (24% of wells), tetrachloroethylene (20%), trichloroethylene (18%), chloroform (9%), and 1,2-dichloroethylene (5%). The spatial distributions of trichloroethylene, chloroform and other volatile organic compounds in the upper glacial aquifer are directly correlated with population density in the two-county area. (USGS)