Transport and Storage of Metal-Contaminated Sediments from Historical Zn–Pb Mining in Elm Creek, Picher, Oklahoma

This study investigated transport and storage of trace metal-contaminated sediments in Elm Creek, in the Tar Creek Superfund Site in northeastern Oklahoma, to evaluate contamination risk from historical Pb–Zn mining and remediation effectiveness at the Bird Dog site. Channel bed sediments were sampled quarterly over 16 months at Bird Dog South (BDS), immediately downstream of a remediated chat pile, Distal West (DW), 2.1 river km (R-km) downstream, and at nine sites extending 15 km toward the Neosho River. Alluvial deposits were cored at six wetland transects between BDS and DW and at five downstream floodplain transects. Discharge, turbidity, and rainfall monitoring at DW enabled flux estimation for 12 storm events. Mean BDS concentrations of Cd (192 mg kg −1 ), Pb (13,500 mg kg −1 ), and Zn (36,300 mg kg −1 ) exceeded regulatory thresholds by one to two orders of magnitude. Concentrations declined exponentially downstream (r 2 = 0.64–0.86), with Zn persisting above the consensus-based probable effects concentration threshold at 13 km. The aggraded wetland segment stores contaminated sediment to depths exceeding 1 m and widths up to 66 m, a large remobilizable inventory. Downstream deposits contain contaminated sediment to at least R-km 4.7 with bench and floodplain erosion posing lateral risk. Low sediment flux at DW (< 0.06 Mg day −1 ) confirms a storage-dominated system governed by retention basins, beaver dam complexes, and low-gradient wetland conditions. Elm Creek currently functions as a contaminant sink, but contaminated alluvial storage in both the near-source aggraded segment and downstream floodplains represents a persistent risk contingent on the continued performance of engineered and natural retention features during extreme events. A conceptual model of retention mechanisms and system vulnerability is presented to support adaptive management of analogous post-mining headwater systems.