Numerical rating model using a geographic information system to determine the vulnerability of water from public supply wells in New Jersey to contamination by pesticides

The vulnerability of water from public supply wells to contamination by pesticides was evaluated by a numerical rating model in conjunction with a geographic information system. The model can be used by regulatory agencies to determine if waivers for monitoring of pesticides can be given if a well is not vulnerable. The vulnerability of a well to contamination by pesticides is defined by (1) the sensitivity of the hydrogeologic system and (2) the intensity of pesticide use in sensitive parts of the aquifer system. Three variables were used to predict aquifer sensitivity; distance of a well from the outcrop area, soil organic matter content, and depth to the top of the open interval of the well. Three variables were used to predict pesticide-use intensity near wells that are sensitive to contamination; predominant land use near the well, distance from the nearest agricultural area, and distance from the nearest golf course.;Well construction and location data were determined for 1,945 public supply wells in New Jersey in three different aquifer types: (1) Coastal Plain, (2) glacial, and (3) bedrock. About 25 percent of the public supply wells are not sensitive to contamination from human activities. About 3 percent of public supply wells are ranked in the high sensitivity and high intensity group. Predicted model results were validated by analyzing water samples for pesticides and nitrates from a stratified-random subset of public supply wells. Pesticides were detected in water from 6 of 90 wells; concentrations were at or near detection levels and below maximum contaminant levels or health advisories. All 6 wells containing pesticides were in the moderate to high sensitivity group and all but 1 were in the high pesticide-use intensity groups.