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ARSENIC IN DRINKING WATER SUPPLY WELLS: A MULTI-AGENCY, COMMUNITY-BASED, RESEARCH PROJECT
PULS, R. ARSENIC IN DRINKING WATER SUPPLY WELLS: A MULTI-AGENCY, COMMUNITY-BASED, RESEARCH PROJECT. Presented at 2nd International Conference on Environmental Science and Technology, Houston, TX, August 19 - 22, 2006.
To inform the public.
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 (µg/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 µg/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 µg/L. With implementation of the new MCL this year, 18 of the 32 wells exceed the allowable concentration of arsenic. 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 existing water supply wells to isolate arsenic-bearing strata in these aquifers. If successful, this approach 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. Additionally, an understanding of arsenic mobilization mechanisms in an aquifer would permit consideration of in situ treatment approaches for the immobilization of arsenic onto aquifer sediments. These latter two approaches are typically 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 paper summarizes the results of a study which addressed the following issues: systematic geologic characterization, discrete-interval well sampling, zonal isolation for well restoration and potential strategies for in situ treatment. This has been a collaborative effort between EPA-ORD, the city of Norman, Oklahoma State University, and the U.S. Geological Survey.