INVESTIGATION OF LEAD DISPERSAL IN GROUNDWATER ASSOCIATED WITH THE TAR CREEK SUPERFUND SITE USING STABLE LEAD ISOTOPE RATIO

The Tri-State Mining District (TSMD) of Ottawa County, Oklahoma, Cherokee County, Kansas, and Jasper County, Missouri was a major site of mining for Pb and Zn ores in the first half of the twentieth century. The Oklahoma portion of the TSMD is called the Tar Creek Superfund Site (TCSS), which is approximately 40 square miles in size and centers on the town of Picher, Oklahoma. Significant releases of hazardous substances from the TCSS- Pb, Cd, and Zn, in particular- have been documented to occur as a result of historical mining practices. Importantly, Pb contamination of groundwater within the Boone aquifer has occurred as a result of weathering of sulfide minerals. The Boone aquifer consists of highly fractured carbonate rocks and crops out as springs in several locations in Ottawa County. An assessment of heavy metal contamination of spring water and associated plants revealed that Pb had accumulated in plants growing in spring water at levels that substantially exceeded background. Additionally, a significant, negative correlation existed between the concentration of heavy metals in spring water and linear distance from the Superfund. These data suggested that movement of contaminated groundwater away from the Superfund resulted in increased metal concentrations in spring water outcropping from the Boone aquifer. The purpose of the present study was to isotopically fingerprint the source of contamination in spring water using stable Pb-isotope ratios in order to test the pathway of exposure from the Superfund to the springs via groundwater. The use of Pb isotopes in sourcing contaminants is well established and is ideal for use in source-fingerprinting as it is a non-essential metal whose isotopic composition is not significantly affected by physico-chemical fractionation processes. Results were compared to Pb isotopic data for alkyl-Pb additives, various North American coals, and background values for crustal weathering products.