Apportioning Mining Waste at a Superfund Site Using Four-Component Linear Mixing: Lower Area One, Butte, Montana, USA

Abstract

Lower area one (LAO), a level section of the floodplain of Silver Bow Creek in Butte, Montana, was used for the disposal of tailings and wastes from a number of milling and smelting operations starting in the 1870s. Several entities including the Colorado Smelter, Butte Reduction Works, Domestic Manganese Development Company (all Butte, MT), and the United States government contributed a variety of milling, smelting, and stockpiling wastes to LAO. In addition to the direct disposal of waste, fluvial deposition of Ag tailings and alluvium from Missoula Gulch also occurred at LAO. Determination of relative volumetric contribution from remaining/successor Potentially Responsible Party (PRPs) arose as part of a larger Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) litigation of the Butte-Clark Fork River Superfund complex. Historical documents, aerial photographs, and geochemical and stratigraphic data were used to develop a four-component linear mixing model based on the concentrations of Cu, Pb, and Mn in the apportionable units. Following the four-component division of Cu, Mn, and Ag/Zn wastes, Ag and Zn were discriminated from each other based on Hg concentrations. The calculations resulted in a quantitative volumetric apportionment of LAO, consisting of 34% Cu tailings, 32% Mn tailings and ore, 27% Ag tailings, and 7% Zn tailings.