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EVIDENCE FOR METAL ATTENUATION IN ACID MINE WATER BY SULFATE REDUCTION, PENN MINE, CALAVERAS COUNTY, CALIFORNIA
Citation:
CHURCH, C. D., C. N. ALPERS, R. O. RYE, AND R. T. WILKIN. EVIDENCE FOR METAL ATTENUATION IN ACID MINE WATER BY SULFATE REDUCTION, PENN MINE, CALAVERAS COUNTY, CALIFORNIA. Presented at 86th American Association for the Advancement of Science Annual Meeting, Ashland, OR, June 12 - 16, 2005.
Impact/Purpose:
To inform the public.
Description:
The Penn Mine in Calaveras County, California, produced Cu from massive sulfide ores from 1861 to 1953. Mine wastes were removed to a landfill during the late 1990s, improving surface-water quality, but deep mine workings were not remediated and contain metalliferous water with pH near 4. Sediments recovered from the flooded mine workings were cultured for anaerobic bacteria over a range of pH (4-7.5). The molecular biology of sediments and cultures were studied to determine whether sulfate-reducing bacteria (SRB) were active within the Penn Mine in acidic conditions previously not documented for SRB. Our data show strong evidence that sulfate reduction and associated metal attenuation are occurring in the pH 4 environment of the Penn Mine underground workings. Water-chemistry analyses reveal: (1) preferential complexation and precipitation by H2S of Cu and Cd, relative to Zn; (2) stable isotope ratios of 34S/32S and 18O/16O in dissolved SO4 that are 2-3 permil heavier in the mine water, relative to surface waters; (3) reduction/oxidation conditions and dissolved gas concentrations consistent with conditions to support anaerobic processes such as sulfate reduction. SEM analyses of sediment show 1.5-micrometer, spherical ZnS precipitates. PLFA and DGGE analyses of Penn Mine sediment show a high biomass level with a moderately diverse community composed primarily of iron- and sulfate-reducing bacteria. Cultures of sediment from the mine removed dissolved sulfate from solution at pH values near-neutral and near 4, forming precipitates of either iron sulfide or elemental sulfur. DGGE analysis of the cultures likewise showed the presence of SRB.