HYDROUS FERRIC OXIDE TRANSPORT PROCESSES DURING FLOOD EVENTS: EXAMPLES FROM THE TAR CREEK SUPERFUND SITE

Mine waste (chat) piles at the Tar Creek Superfund Site in Northeast Oklahoma have elevated concentrations of Pb, Zn, and Cd. Metals are transported away from the site and enter Tar Creek through chat pile run-off, seepage from underground mines, and leaching from chat within the streambed. Metal loading via these pathways contributes to ecosystem degradation and has raised exposure concerns in communities along Tar Creek during large flood events. This research examines the metal concentrations adsorbed to hydrous ferric oxides (HFOs) collected within Tar Creek and deposited on tree bark and on floodplain soils after the major summer 2007 flood event of the Tar Creek and Neosho River systems. In addition to a suite of floodplain soils collected before and after the July 2007 flood event, samples of HFOs that were filter collected from within the channel of Tar Creek along with HFO-coated tree bark. This bark was analyzed in situ using field portable X-ray fluorescence (FP-XRF) at three sites downstream of chat pile and mine seepage inputs. HFOs preserved in floodplain soils and tree bark act as metal sinks and may be a major constituent of metals mobilized during flooding events. FP-XRF results show covariance between [Pb], [Zn] and [Fe], suggesting heavy metal affinity for HFOs while Ca varies inversely with Fe as a function of height above the bark/soil interface. Lead to Zn ratios on tree bark decrease as a function of distance downstream from sources. These results suggest that HFOs serve as an important end-member metal sink in watershed wide transport processes and that Pb's higher tendency toward adsorption causes it to be retained in soils and bark closer to the chat piles. Sequential extraction (SE) tests will be used to determine if subsequent flood events could cause metal remobilization from these HFOs while X-ray diffraction (XRD) analyses will be used to complement SE data to identify mineral phases and the extent of HFO crystallization. Ultimately, data from these three sources of HFOs will be incorporated into a fate and transport model using principal component analysis and grain size distributions to evaluate the extent of metal transport out of stream channels by HFO deposition.