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ARSENIC IN DRINKING WATER SUPPLY WELLS: A MULTI-AGENCY COMMUNITY-BASED, RESEARCH PROJECT
Citation:
PULS, R., S. J. SMITH, S. PAXTON, AND G. WELBORN. ARSENIC IN DRINKING WATER SUPPLY WELLS: A MULTI-AGENCY COMMUNITY-BASED, RESEARCH PROJECT. Presented at A City Officials Meeting, Norman, OK, February 01, 2007.
Impact/Purpose:
To inform the public.
Description:
Studies have indicated that arsenic concentrations greater than the new U.S. Environmental Protection Agency (EPA) maximum contaminant level (MCL) concentration of 10 micrograms per liter (ųg/L) occur in numerous aquifers around the United States. One such aquifer is the Central Oklahoma aquifer, which supplies drinking water to numerous communities in central Oklahoma. Concentrations as high as 230 ųg/L have been reported in some drinking water supply wells from this aquifer. The city of Norman, like most other affected cities, is actively seeking a cost-effective solution to the arsenic problem. Only six of the city’s 32 wells exceeded the old MCL of 50 ųg/L. With implementation of the new MCL in 2006, 18 of the 32 wells exceed the allowable concentration of arsenic (10 ųg/L). Arsenic-bearing shaly sandstones appear to be the source of the arsenic. It may be possible to isolate these arsenic-bearing zones from water supply wells, enabling production of water that complies with drinking water standards. It is hypothesized that geologic mapping together with detailed hydrogeochemical investigations will yield correlations which predict high arsenic occurrence for the siting of new drinking water production wells. More data and methods to assess the specific distribution, speciation, and mode of transport of arsenic in aquifers are needed to improve our predictions for arsenic occurrence in water supply wells. Research is also needed to assess whether we can retrofit or restore existing water supply wells to either isolate arsenic-bearing zones in these aquifers or use in situ treatment techniques to remove the arsenic from the water. If successful, these approaches would eliminate the need for expensive well head treatment of arsenic for public drinking water supplies. This would significantly reduce the costs of bringing public water supplies into compliance with the lower drinking water standard for arsenic. A thorough understanding of arsenic mobilization mechanisms in an aquifer is essential for consideration of in situ treatment approaches for the immobilization of arsenic onto aquifer sediments. These latter two approaches may be more cost effective in dealing with high arsenic concentrations than surface treatment approaches involving expendable treatment media and disposal of arsenic bearing residuals from surface treatment technologies. This has been a collaborative effort between Environmental Protection Agency’s Office of Research & Development (Robert S. Kerr Environmental Research Center in Ada, OK), the city of Norman, Oklahoma State University, and the U.S. Geological Survey.