Abstract: A permeable reactive barrier was installed in August 1995 at the Nickel Rim Mine near Sudbury, Ontario, Canada, for the passive remediation of groundwater contaminated with acid mine drainage. The reactive component of the barrier consists of a mixture of municipal and leaf compost and wood chips: the organic material promotes bacterially-mediated sulphate reduction. Hydrogen sulphide, a product of sulphate reduction, may then complex with aqueous ferrous iron and precipitate as iron sulphide. This study presents the solid phase sulphur chemistry of the reactive wall after two years of operation, and discusses the formation and accumulation of iron sulphide minerals in the reactive material. The results from the solid-phase chemical analysis of core samples indicate that there is an accumulation of reduced inorganic sulphur in the reactive wall, with levels reaching 190 mu mol g (super -1) (dry weight) by July 1997.

Abstract: Three alkaline materials were investigated for their suitability to treat acid mine drainage generated by a research facility located at a remote site in northern Minnesota. The materials investigated were hydrated lime, sodium hydroxide, and magnesium hydroxide. All three reagents were successful at raising pH and removing trace metals from the drainage, but the magnesium hydroxide had the added benefit of producing a maximum pH of approximately 9.5, while the other two reagents resulted in pH values of 12 and greater. In addition, the magnesium hydroxide was available as a high solid content slurry (58%) which simplified application and handling, and which produced the lowest volume of sludge of the materials tested.

Abstract: Permeable reactive barriers are a promising new approach to the treatment of dissolved contaminants in aquifers. This technology has progressed rapidly from laboratory studies to full-scale implementation over the past decade. Laboratory treatability studies indicate the potential for treatment of a large number of inorganic contaminants, including As, Cd, Cr, Cu, Hg, Fe, Mn, Mo, Ni, Pb, Se, Tc, U, V, NO3, PO4, and SO4. Small scale field studies have indicated the potential for treatment of Cd, Cr, Cu, Fe, Ni, Pb, NO3, PO4, and SO4. Permeable reactive barriers have been used in full-scale installations for the treatment of hexavalent chromium, dissolved constituents associated with acid-mine drainage, including SO4, Fe, Ni, Co and Zn, and dissolved nutrients, including nitrate and phosphate. A full-scale barrier designed to prevent the release of contaminants associated with inactive mine tailings impoundment was installed at the Nickel Rim mine site in Canada in August 1995. This reactive barrier removes Fe, SO,, Ni and other metals. The effluent from the barrier is neutral in pH and contains no acid-generating potential, and dissolved metal concentrations are below regulatory guidelines. A full-scale reactive barrier was installed to treat Cr(VI) and halogenated hydrocarbons at the US Coast Guard site in Elizabeth City, North Carolina, USA in June 1996. This barrier removes Cr(VI) from >8 mg l(-1) to <0.01 mg l(-1).