U.S. Geological Survey Toxic Substances Hydrology Program--Proceedings of the Technical Meeting, Colorado Springs, Colorado, September 20-24, 1993, Water-Resources Investigations Report 94-4015

Vulnerability of Water from Public Supply Wells to Contamination by Pesticides, Potomac-Raritan-Magothy Aquifer System, New Jersey Coastal Plain

Abstract

A numerical rating model used in conjunction with hydrogeologic, land-use, and water-quality data stored in a geographic information system was developed to rank 558 public supply wells screened in the Potomac-Raritan-Magothy aquifer system in the New Jersey Coastal Plain into groups of high, medium, and low vulnerability to contamination by pesticides. The vulnerability of water from public supply wells to contamination by pesticides is defined by variables describing the (1) sensitivity of the aquifer to contamination and (2) intensity of pesticide use in areas where the aquifer is sensitive. The results of the model indicated that 305 wells were of low vulnerability, 237 were moderately vulnerable, and 16 were highly vulnerable to contamination. Because analyses for pesticides in water samples are scarce, the concentration of nitrate in water samples was used as a surrogate to develop and test the accuracy of the model. Results of statistical tests indicate that the concentration of nitrate is a significant indicator of aquifer sensitivity, pesticide-use intensity, and the presence of pesticides in ground water. Results of the rating model indicate that water from only 1 of the 138 sampled wells that were ranked as low vulnerability contained nitrate as nitrogen in concentrations larger than 0.5 milligrams/L. Concentrations of nitrate in water samples were significantly larger in the medium- and high-vulnerability groups than in the low-vulnerability group.