METAL FATE AND TRANSPORT STUDIES AT THE TAR CREEK SUPERFUND SITE

The Tar Creek Superfund Site in northeastern Oklahoma is heavily impacted from decades of lead and zinc mining in the Tri-State Mining District that started in the early 1900s and lasted until around 1970. A notable legacy of these activities is the presence of large mounds of mine waste (known locally as chat) containing elevated concentrations of zinc, lead and cadmium. Runoff from these piles, together with acid mine drainage (AMD) from the abandoned mines, contribute to metal loading into the Tar Creek watershed. As part of a broader investigation of potential children’s health impacts from exposure to these metals in mining materials, we assessed the fate and transport of major contaminant metals in the Tar Creek watershed.

This presentation will provide an overview of our key findings. In particular, we found highly elevated concentrations of zinc, lead and cadmium in size-fractionated chat, especially in the smallest size fractions most relevant for human exposure, and a high degree of metal lability and bioaccessibility in those fractions. With respect to metal loadings into Tar Creek, chat pile runoff and AMD were both major contributors, with the relative contributions varying among metals. Subsurface groundwater inputs were also substantial contributors to flow and metal loading. In-stream transport of zinc, lead and cadmium were controlled to varying degrees by hydrous ferric oxides (HFOs), and solid-phase concentrations of HFO-bound metals were highly elevated, which has implications for downstream mobility and transport into the floodplain. Comparisons with historical data show that while metal concentrations in AMD have decreased substantially in recent decades, the chemical composition of chat pile runoff has remained relatively constant, suggesting less attenuation and increased relative importance of chat pile runoff. Our results highlight the importance of simultaneously addressing surface and subsurface contamination from both AMD and chat pile runoff in this watershed.