Water-quality data from public and private drinkingwater supply wells that were sampled from October 1997 through March 2001 in Suffolk County, New York were evaluated to define the occurrence and concentrations of arsenic throughout the county. The data bases of the Suffolk County Water Authority (SCWA) and the Suffolk County Department of Health Services (SCDHS) included 14 wells at which arsenic concentrations approached or exceeded the 2002 U.S. Environmental Protection Agency (USEPA)

more »

... ng-water guideline of 10 micrograms per liter (µg/L). As a followup, 19 wells were sampled from June through August 2002; 7 were wells previously reported to have had high arsenic concentrations; 7 were near other wells reported to have high concentrations, and the remaining 5 were in areas where detectable concentrations of arsenic were suspected. Arsenic concentrations near 10 µg/L were detected at only 2 of the 19 wells sampled; arsenic concentrations in samples from the remaining 17 wells were reported as less than the USGS Central Laboratory reporting limits of 2 µg/L or 4 µg/L. The elevated concentrations previously reported (1997 through 2001) for at least three of the wells were due to incompletely flushed carbon filters in the supply-well system or were typographical errors. A decrease in arsenic concentration was indicated at six of the seven resampled wells; no reasons are apparent. Arsenic concentrations in ground water that exceed drinking-water guidelines were found only at one site. On the basis of limited sampling data available for this study, the concentrations of arsenic above drinking-water standards (10 µg/L) do not appear to indicate a countywide problem with regards to arsenic concentrations in ground water.