Characterization of residual solids from mine water passive treatment oxidation ponds at the tar creek superfund site, Oklahoma, USA: Potential for reuse or disposal
Justine I. McCann, Robert W. Nairn
Abstract
Ecologically engineered passive treatment systems have been successfully implemented world-wide to decrease concentrations of ecotoxic metals in mine drainage without continuous energy or material inputs. Typical design life of such treatment systems is approximately 20 years, at which point rehabilitative maintenance must occur. For example, oxidation ponds, designed to accumulate iron (oxyhydr)oxide solids, must be dredged to sustain effective hydraulic retention time, creating large volumes of potentially hazardous waste. In this study, total recoverable and leachable metals in iron (oxyhydr)oxide solids from the oxidation ponds of two multi-cell passive treatment systems in the historic and now derelict Tri-State Lead-Zinc Mining District in Ottawa County, Oklahoma, United States were characterized using several batch leaching tests. This assessment informs potential disposal and reuse scenarios for the solids once they have been removed from the systems. Solids leached nonhazardous concentrations of metals under Resource Conservation and Recovery Act guidelines. However, some metals exceeded Oklahoma Water Resources Board criteria for protection of public water supplies, and total metals exceeded some consensus-based toxicity benchmarks for soils and sediments. Beneficial reuse plans for the iron (oxyhydr)oxides must consider these potential risks.