THE DISTRIBUTION AND PARTITIONING OF METALS AT THE ANACONDA SMELTER SITE, MONTANA

One of the largest smelter and mining contaminated sites in the United States is located in Anaconda, Montana, and has been designated a U.S. Environmental Protection Agency Superfund Complex. Smelting operations in Anaconda continued for approximately nine decades, generating vast quantities of waste materials and tailings. These products of the smelting operations have caused severe degradation of the local and surrounding soils (700 km²), and contamination of groundwater and the Clark Fork River. The principal metal contaminants include arsenic, cadmium, copper, lead and zinc. This presentation will summarize our studies designed to investigate the geochemical parameters and processes responsible for determining the mobility and bioavailability of the contaminants. Four soil cores were collected proximally to the smelter-tailing ponds. The cores extended to depths from 0.63m to 2.5m, and were sampled for analysis at 30-50cm intervals. All soil samples were sieved to obtain a <0.25mm size fraction, then a sequential extraction procedure following that of Tessier et al. (Analytical Chemistry, 1979) was completed. In addition, soils samples and residues from the extraction experiments were acid digested following EPA Method 3050B. Inductively coupled plasma spectroscopy was used to analyze for As, Cd, Cu, Pb and Zn within the sequential extraction extracts and acid digestion solutions. For completeness, Mn, Al, Fe, K, Ni, Sr and Co concentrations were also determined. As anticipated, metal concentrations varied as a function of depth (redox state) and distance from the smelter-tailing ponds. Cadmium was associated with the exchangeable fraction, whereas As and Pb concentrations were highest in the iron- and manganese-oxide and organic fractions. Further experiments will investigate the distribution of the metals as a function of grain size. All experimental results will be modeled to help predict metal mobility under the relevant vadose zone conditions.