Assessment of Amendments in the Reclamation of an Abandoned Mine in Montana

Abstract

There are numerous no-responsible-party abandoned mine sites on public lands in western Montana that have been inactive for more than 70 years, yet remain bare of vegetation and drain acidic water to mountain streams. Montana lacks widespread availability of organic materials commonly used in mine reclamation and there is limited information available regarding the efficacy of alternative organic mine reclamation amendments. Replicated field and laboratory studies were undertaken to assess how various surface treatments influence metal mobility and restoration of tailing piles along a second order tributary to the Blackfoot River. Laboratory incubations were carried out by treating tailings with nothing (control), aged log-yard waste, or composted sewage sludge (Eko Kompost, Missoula, MT) with or without lime. After four weeks, tailings were analyzed for pH and exchangeable Pb, Cu, and Fe. Field plots (2 m x 4 m) were treated as above, seeded with native wheat grass species, and analyzed for pH, exchangeable Pb, Cu, and Fe, microbial biomass, and vegetative cover after eight weeks and 12 months. All liming treatments significantly increased pH and reduced levels of exchangeable metals. Aged log-yard waste alone had little or no effect on pH or levels of exchangeable metals and actually increased levels of exchangeable Pb. Compost applications had only a slight effect on pH, but significantly reduced levels of exchangeable metals and increased levels of microbial biomass. Compost plus lime resulted in the lowest levels of exchangeable metals and greatest vegetative cover. The ability of compost to reduce metal mobility and increase microbial and vegetative activity without a significant change in pH indicate that nutrient availability and reduced metal bioavailability play an important role in site restoration.