Naturally occurring arsenic in sandstone aquifer water supply wells of northeastern Wisconsin

The U.S. Environmental Protection Agency (EPA) maximum contaminant level (MCL) of 50 microgram/L for arsenic was exceeded in 86 of 2125 water supply wells sampled over a broad geographic range in parts of Brown, Outagamie, and Winnebago Counties, Wisconsin. The hydrologic and geochemical properties...

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Bibliographic Details
Published in:Ground water monitoring & remediation 1999-05, Vol.19 (2), p.114-121
Main Authors: Burkel, R.S, Stoll, R.C
Format: Article
Language:English
Subjects:
Aquifers
Arsenic
Construction
Contaminants
Dolomite
drinking water
Galena
Geochemistry
Groundwater
Guidelines
Monitoring
Remediation
Sandstone
spatial distribution
vertical distribution
water quality
Water supply
Wells
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Summary:The U.S. Environmental Protection Agency (EPA) maximum contaminant level (MCL) of 50 microgram/L for arsenic was exceeded in 86 of 2125 water supply wells sampled over a broad geographic range in parts of Brown, Outagamie, and Winnebago Counties, Wisconsin. The hydrologic and geochemical properties of the area were examined and the source of arsenic was determined to be natural. Ground water collected from two geologic formations, the St. Peter Sandstone and the overlying Platteville/Galena Dolomite, was found to be the principal source of the elevated arsenic concentrations. These two formations supply a large portion of eastern Wisconsin private wells with their drinking water. Three wells were found within Outagamie County to have an unusually low pH. Results suggest that the cause of the low pH in these wells is of natural origin induced by the oxidation of iron sulfide minerals. In this reaction iron sulfide minerals are oxidized, forming sulfuric acid causing a low pH and a high concentration of various metals to leach from native rock formations into the water supply. Based on the data gathered from this study. an arsenic advisory area was designated for both Outagamie and Winnebago Counties. Guidelines were developed for well drillers and owners constructing new wells within the advisory area to reduce the likelihood of arsenic presence in the water supply. Fifteen wells containing arsenic exceeding the MCL were successfully reconstructed or new wells were constructed based on the guidelines developed. These constructions substantially reduced arsenic levels in the well water supplies.
ISSN:1069-3629
1745-6592
DOI:10.1111/j.1745-6592.1999.tb00212.x