An Assessment of Metals Distribution and Transport in Groundwater Beneath the Diked Sediment Disposal Area, DePue Wildlife Management Area, Illinois

Potential toxic metal (Zn, Cd, Pb, Cu) contamination of groundwater at the periodically flooded DePue Dredged Sediment Disposal Area (DSDA), was assessed through the collection of groundwater and soil samples and water level data, geochemical modeling, and leaching and microcosm experiments. The median Zn concentrations in groundwater at three locations were between 2 and 5 mg/L. There was no evidence that contaminated groundwater has migrated offsite. Based on lake-sediment and soil data, the order of decreasing mobility in the site groundwater was Zn > Cu > Cd > Pb. Small amounts of Zn and Cd (< 2%) were leached from soil samples inside the DSDA in leaching experiments. About half of the dissolved Zn and Cd from groundwater samples can be accounted for by leaching, suggesting desorption was a major control for Zn and Cd. Chemical equilibrium calculations indicated that several reactions, including CdCO3 precipitation, coprecipitation of Zn with CaCO3, and sorption to ferric oxide, may retain the metals in the subsurface. Aqueous Zn concentrations were greatest in aerobic microcosms, lowest in sulfate-reducing microcosms, and intermediate in iron-reducing microcosms. Zinc would thus be expected to be most mobile in DePue soils during the early stages of flooding, when the soils are saturated but before conditions become anaerobic.Illinois Waste Management and Research Centerpublished or submitted for publicationis peer reviewe