ARSENIC IN GROUND WATER IN EASTERN NEW ENGLAND: OCCURRENCE, CONTROLS AND IMPLICATIONS FOR HUMAN HEALTH
Joseph D. Ayotte, Denise L. Montgomery, Sarah M. Flanagan, Keith W. Robinson, and Laura Hayes
U.S. Geological Survey, 361 Commerce Way, Pembroke, NH 03275

In New England, low to moderate (1 to 50 micrograms per liter) concentrations of arsenic are known to occur in ground water, especially in the Eastern part of the region. There is increasing evidence that the source of the arsenic in New England is predominantly natural, originating from minerals within the rocks of the region. However, anthropogenic sources of arsenic (e.g. former pesticide use, treated lumber, manufacturing) may also contribute to ground-water contamination. Data from 88 wells in eastern New England showed that arsenic is more prevalent in water from private bedrock wells than in water from public wells in unconsolidated aquifers. Ground water from unconsolidated aquifers used for public supply accounts for about 33 percent of all drinking water use eastern New England. Water from these aquifers is less likely to be affected by contamination from arsenic (about 3 percent have water with arsenic greater than 10 micrograms per liter) than privately supplied drinking water derived from bedrock aquifers. Water from private wells in bedrock aquifers accounts for about 14 percent of drinking water supplies in the area and is most likely to have arsenic concentrations at levels of concern to human health. Wells located in metasedimentary bedrock units that are described as variably calcareous are most likely to have elevated ground-water concentrations of arsenic compared to water from wells in other rock types. Nearly 30 percent of wells in these rock units had water with arsenic greater than 10 micrograms per liter. Arsenic concentrations were greatest where pH was greater than 7.5 and where dissolved oxygen concentrations were less than 1 milligram per liter. Arsenic was most commonly detected where the ground water was at or near saturation with respect to calcite. Fifty-eight of the 88 wells were sampled twice, 1 to 12 months apart. There was a strong correlation between concentrations for the two samples at each well (Spearman's rho = 0.86, 95% C.I. = 0.76-0.92) indicating that arsenic concentrations in bedrock wells did not change significantly during the interval. Although arsenic concentrations did not relate to any other metals, major ions, age of ground water, or hydraulic parameters, arsenic concentrations were related to major aquifer types (unconsolidated and bedrock) and to water supply types (public and private). From this information and associated water-use information, the total population potentially receiving drinking water with arsenic greater than 10 micrograms per liter was estimated at nearly 90,000 people on public supplies and about 114,000 people on private supplies. Whereas the estimate for the public-supply population will likely decrease because a lower standard will go into effect in 2006, the estimate for the population using unregulated private wells may not.