ARSENIC IN GROUND WATER WELLS IN MAINE
Marc C. Loiselle 1, Robert G. Marvinnney 1, and Andrew E. Smith 2
1 Maine Geological Survey, 22 State House Station, Augusta, ME, 04333-002 2
2 Environmental Toxicology Program, 11 State House Station, Augusta, ME, 04333-0011

In the summer of 1993, residents of the towns of Buxton and Hollis, Maine, became concerned about the persistence of elevated arsenic concentrations (> 0.05 mg/L, the present EPA maximum contaminant level (MCL)) in the drinking water supply for a local school, although the elevated arsenic concentrations had been discovered several years earlier. This concern led to a town-wide survey of arsenic concentrations in over 1200 domestic water supplies. The survey found that over 13-percent of the tested samples had arsenic concentrations in excess of the MCL. Analysis of data on arsenic concentration in groundwater from several sets of random and pseudo-random bedrock wells indicates that 1- to 3-percent of wells in Maine have arsenic concentrations above the present maximum contaminant level (MCL) of 0.050 mg/l and 12- to 13-percent above the proposed standard of 0.010 mg/l. These are comparable to levels found in New Hampshire (Peters and others, 1999) and New Brunswick (Brinsmead, personal communication, 2000), but significantly lower than values in the sample of private wells in the Buxton-Hollis area. Water samples from bedrock wells are much more likely to have elevated arsenic concentrations than dug wells or springs. The distribution of wells with elevated arsenic concentrations is not random. Statewide, the random and pseudo-random wells show a much higher occurrence of elevated concentrations in zones of biotite grade or higher metamorphism or adjacent to igneous intrusions. Several zones of elevated arsenic concentrations can be observed along an axis from northern York County (Buxton and Hollis) through central Kennebec County and in eastern coastal Maine. The arsenic concentration of groundwater is the most likely the result of both natural processes and human activities. A study of historical uses of arsenic in Maine (D'Angelo and others, 1996) showed widespread use of arsenic pesticides between 1920 and 1950, ending in the late 1960s. Conservative estimates indicate that 5 lbs/acre of As were applied to each year to apple orchards and blueberry fields, and 20 lbs/acre applied each year to potato fields. Locally high concentrations of arsenic in groundwater on the scale of kilometers (for example, Northport and Surry) appear to be associated with igneous activity within a belt of sulfidic pelites. An ongoing study of ambient ground water quality in bedrock wells may provide additional information on the source and transport of arsenic in the bedrock flow system.