GROUNDWATER QUALITY OF NEW ENGLAND CRYSTALLINE BEDROCK AQUIFERS

A regional-scale characterization of water quality in crystalline bedrock aquifers in New England and northern New Jersey was done using data from untreated groundwater samples collected from 117 domestic-supply bedrock wells sampled by the U.S. Geological Survey and from 4,775 public-supply bedrock wells sampled for the USEPA Safe Drinking Water Program. About 13 percent of 2,054 wells had concentrations of arsenic greater than the MCL of 10 micrograms per liter, but 22.8 percent of the 492 wells drilled in calcareous metasedimentary bedrock in eastern New England exceeded the MCL. Of 556 uranium samples, 14.2 percent had concentrations of uranium greater than the MCL of 30 micrograms per liter; however, the percentage for the domestic wells was lower at 4.3 percent. Of 4,781 nitrate samples, only 5 samples had nitrate concentrations greater than the MCL of 10 milligrams per liter. Methyl tert Butyl Ether and chloroform were the most frequently detected volatile organic compounds in 86 domestic well samples at 36 and 32.9 percent respectively. Elevated fluoride concentrations (> 2 milligrams per liter) generally occurred in older, high pH (>8) sodium-bicarbonate waters in granitic bedrock. Chloride to bromide ratios indicate that the groundwater was affected by at least three halogen sources: local precipitation and recharge, seawater and connate waters evolved from seawater, and recharge waters affected by road de-icing salts. In untreated groundwater collected from 26 domestic wells, Total Coliform was detected in 19 (73 percent) samples, Escherichia coli was not detected, and coliphage was positively identified in two (8 percent) samples.