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Pesticides, Arsenic, and Radon in Ground Water

Ground water hazards are found as naturally occuring conditions and as contaminants introduced by human activities. In 1989, the MGS published the results of a three-year study of the effect of agricultural practices on ground water quality (Maine Geological Survey, Open-File Report 89-2, Final Report - Pesticides in Ground Water Study). The results indicate that while pesticide residues are present in the ground water in some areas of Maine, concentrations are low.

Arsenic contamination in private wells has come to public attention periodically in New England. In mid-1993, several private wells in Buxton, Maine, were found to have arsenic levels in excess of the EPA MCL (Maximum Contaminant Level) of 50 ppb (parts per billion). (Note: The MCL has more recently been changed to 10 ppb.) This discovery led to town-wide testing and initiation of a State multi-agency study to assess the problem. Using the Maine Department of Human Service's database of arsenic analyses, MGS developed statewide statistics and maps of arsenic distribution. Analyses showed that most populated areas have some elevated concentrations, and that these areas include virtually every geologic setting found in the State, leading to the conclusion that the problem is of statewide significance. The bedrock geology of the State includes some sulfide-bearing rocks that provide a plausible natural source for some of the arsenic, but anthropogenic sources, particularly in the more populated areas, may be significant.

Radon, a decay product of uranium, is a radioactive gas present in nearly all ground water in Maine. It tends to be concentrated in granite and highly metamorphosed rocks. The gas diffuses into ground water as it slowly flows through fractures in the bedrock. When heated or agitated, the gas readily diffuses from the water into the air. The MGS, in association with workers from other state agencies and from the University of Maine, has published or been co-author of several papers pertaining to radon, geology, and human health in Maine.

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Last updated on June 21, 2012

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