Groundwater quality in the Delaware and St. Lawrence River Basins, New York, 2010

Abstract

Water samples were collected from 10 production and domestic wells in the Delaware River Basin in New York and from 20 production and domestic wells in the St. Lawrence River Basin in New York from August through November 2010 to characterize groundwater quality in the basins. The samples were collected and processed by standard U.S. Geological Survey procedures and were analyzed for 147 physiochemical properties and constituents, including major ions, nutrients, trace elements, pesticides, volatile organic compounds (VOCs), radionuclides, and indicator bacteria. The Delaware River Basin covers 2,360 square miles in New York, and is underlain mainly by shale and sandstone bedrock with other types of bedrock present locally. The bedrock is overlain by till in much of the basin, but surficial deposits of saturated sand and gravel are present in some areas. Five of the wells sampled in the Delaware study area are completed in sand and gravel deposits, and five are completed in bedrock. Groundwater in the Delaware study area was typically neutral or slightly acidic; the water typically was soft. Bicarbonate, chloride, and calcium were the major ions with the greatest median concentrations; the dominant nutrient was nitrate. Strontium, barium, iron, and boron were the trace elements with the highest median concentrations. Radon was detected in all samples with activities greater than 300 picocuries per liter; the greatest radon activities were in samples from bedrock wells. Four pesticides, all herbicides or their degradates, were detected in four samples at trace levels; five VOCs, including four trihalomethanes and tetrachloromethane, were detected in two samples. Coliform bacteria were detected in five samples, but fecal coliform bacteria and Escherichia coli ( E. coli ) were not detected in any samples from the Delaware study area. The St. Lawrence River Basin covers 5,650 square miles in New York. The St. Lawrence River Basin in New York is underlain by crystalline, carbonate, and sandstone bedrock. The bedrock is overlain by till or lacustrine and marine deposits in much of the basin. Surficial deposits of saturated sand and gravel are present locally, but most wells in the basin are completed in bedrock. Five of the wells sampled in the St. Lawrence study area are completed in sand and gravel deposits, and 15 are completed in bedrock. Groundwater in the St. Lawrence study area was typically neutral or slightly basic; the water typically was hard. Bicarbonate, sulfate, and calcium were the major ions with the greatest median concentrations; the dominant nutrient was nitrate. Strontium, iron, barium, and boron were the trace elements with the highest median concentrations. Radon was detected in two-thirds of samples with activities greater than 300 picocuries per liter; the greatest radon activities were in samples from bedrock wells. Seven pesticides, including 5 herbicides, an herbicide degradate, and an insecticide, were detected in 11 samples at trace levels; 3 VOCs (tetrachloroethene, toluene, and trichloromethane, or chloroform) were detected in 2 samples. Coliform bacteria were detected in 7 samples, and E. coli were detected in two samples in the St. Lawrence study area. Water quality in both study areas is generally good, but concentrations of some constituents equaled or exceeded current or proposed Federal or New York State drinking-water standards. The standards exceeded are color (one sample in the St. Lawrence study area), pH (three samples in the Delaware study area), sodium (one sample in the St. Lawrence study area), total dissolved solids (one sample in the St. Lawrence study area), aluminum (one sample in the Delaware study area and one sample in the St. Lawrence study area), iron (seven samples in the St. Lawrence study area), manganese (one sample in the Delaware study area and five samples in the St. Lawrence study area), gross alpha radioactivity (one sample in the St. Lawrence study area), radon-222 (10 samples in the Delaware study area and 14 samples in the St. Lawrence study area), and bacteria (5 samples in the Delaware study area and 10 samples in the St. Lawrence study area). E. coli bacteria were detected in samples from two wells in the St. Lawrence study area. Concentrations of chloride, fluoride, sulfate, nitrate, nitrite, antimony, arsenic, barium, beryllium, cadmium, chromium, copper, lead, mercury, selenium, silver, thallium, zinc, and uranium did not exceed existing drinking-water standards in any of the samples collected.