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ACCUMULATION RATE OF MICROBIAL BIOMASS AT TWO PERMEABLE REACTIVE BARRIER SITES
Citation:
Wilkin*, R T., G W. Sewell*, AND R W. Puls*. ACCUMULATION RATE OF MICROBIAL BIOMASS AT TWO PERMEABLE REACTIVE BARRIER SITES. Presented at American Geophysical Union, San Francisco, CA, 12/31/2001.
Description:
Accumulation of mineral precipitates and microbial biomass are key factors that impact the long-term performance of in-situ Permeable Reactive Barriers for treating contaminated groundwater. Both processes can impact remedial performance by decreasing zero-valent iron reactivity and permeability. Results are presented from solid-phase and groundwater monitoring studies conducted at two Permeable Reactive Barrier sites: U.S. Coast Guard Support Center (Elizabeth City, North Carolina) and the Denver Federal Center (Lakewood, Colorado). At both sites barrier installations have been in place for approximately five years. Over this period, consistent patterns of spatially heterogeneous microbial biomass accumulation are observed at these sites. The iron/aquifer interface witnesses the greatest accumulation of microbial biomass and mineral precipitates. There accumulation rates are a factor of 3 to 10 times greater than mid-wall or downgradient regions. Estimates of porosity loss due to mineral and biomass buildup range from about 1 to 5% per year of the initial available volume. Phospholipid fatty acid profiles indicate that the PRB biomass is dominated by biomarkers indicative of anaerobic sulfate-reducing or iron-reducing bacteria. This result is in agreement with acid-volatile sulfide concentrations that strongly correlate with biomass concentrations. Upgradient groundwater chemistry and flow rate appear to be the main factors that control the rate (and type) of mineral precipitate formation as well as the rate of biomass accumulation.