CHARACTERIZATION OF TOXIC METAL TRANSPORT PROCESSES DOWNSTREAM OF THE TAR CREEK SUPERFUND SITE

The mine waste (chat) piles at the Tar Creek Superfund Site in Northeast Oklahoma have elevated concentrations of Pb, Zn, and Cd and are a major source of metal contamination to the area. Runoff from these piles, seepage from underground mines and leaching from chat within the streambed, contribute to metal loading into Tar Creek, which drains a portion of the Superfund Site, and ultimately into the Neosho River. The objective of this research is to identify processes that control the transport of these metals within Tar Creek and the Neosho River. Sediment cores were collected at several locations along Tar Creek and in the Neosho River near the confluence with Tar Creek, as well as soil samples from the Tar Creek floodplain, to determine the extent of contamination and relative mobility of Pb, Zn and Cd. Hydrous ferric oxides (HFOs) also were collected at several locations along Tar Creek to evaluate their role in removal of metals from the water column and in downstream particulate metal transport. Total metal concentrations were analyzed using x-ray fluorescence and sediment mineralogy was characterized using x-ray diffraction. Total Pb and Zn concentrations in Tar Creek sediments 10 km downstream from the mining area were generally correlated and exhibited several peaks with depth (up to 450 and 5500 ppm, respectively). These peak concentrations are only two times lower than average concentrations in bulk chat samples (9000 ppm Zn and 650 ppm Pb) and are considerably higher than background concentrations in the Neosho River (21 ppm Pb and 130 ppm Zn). Deposition of metals from Tar Creek into Neosho River sediments resulted in elevated metal concentrations downstream of the confluence, up to a factor of 4 higher for Zn. Average Zn was consistently present at concentrations approximately 15 times higher than average Pb in Tar Creek sediment cores, similar to the ratio in bulk chat samples. Metal concentrations in floodplain soils collected within 35 m of the creek also were elevated relative to background concentrations (up to 200-300 ppm Pb) and appeared to decrease with increasing distance from the Superfund Site. Further research will include additional sediment sampling and analysis to further characterize the spatial and historical extent of metal contamination in the Neosho River and the role of HFOs in metal mobility.