The Speciation of Groundwater Contaminated with Coal Pile Leachate at the Savannah River Site, South Carolina

Modeling the transport of contaminant metals and designing systems for their remediation requires an understanding of the metal's speciation. Thus, analysis of contaminant speciation and evaluation of the processes that can change the speciation should be done during characterization of the contaminated site. This approach is being used at the Savannah River Site for a metals contaminated site that will serve as a test platform for metals remediation technologies. The site is adjacent to a coal storage pile and the basin that contains the coal pile runoff. A network of well clusters allows definition of the plume, including profiles of contamination with depth. The groundwater is acidic (pH ∼ 2) and contains high concentrations of sulfate (up to 2300 mg/l) and metals, with chromium, nickel, cadmium and lead exceeding drinking water standards. Aluminum and total iron concentrations range up to 1326 mg/l and 7991 mg/l, respectively. Speciation calculations on dissolved contaminants indicate that as much as 65% of the lead, 54% of the cadmium, and 34% of the nickel may be present in sulfate complexes. Chromium occurs predominantly as Cr+3. There is evidence that some contaminant metals may be associated with colloidal material. Contamination in the groundwater is stratified with concentrations decreasing over a depth range of 3 meters (10 feet). Fluid-rock interactions explain the non-uniform behavior of dissolved components with depth. Mass balance considerations suggest that the interactions are dominated by Kaolinite dissolution coupled with precipitation of phases containing aluminum, ferric iron, silica, and sulfate, as well as co- precipitation of contaminant metals