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Environmental Health - Toxic Substances

Toxics Program Remediation Activities

Natural Attenuation of Chlorinated Ethenes in a Seasonally Cold Environment, Fairbanks, Alaska

  • Feasibility Studies
  • Natural Attenuation Evaluation
  • Site Characterization

Alaska Department of Transportation and Public Facilities Peger Road Operations and Maintenance Facility, Fairbanks, Alaska

Partners Alaska Department of Environmental Conservation
  • Monitored Natural Attenuation
  • Enhanced Biodegradation (Source Area Remediation)
  • Chlorinated Solvents (trichloroethene TCE)
  • Hydrocarbons

RDX concentrations, redox conditions, and HCO3- concentrations in the shallow aquifer at Site A, Operable Unit 1, NSB Bangor during May 2002. Cold weather soil sampling at the Alaska Department of Transportation and Public Facilities Peger Road Operations and Maintenance Facility, Fairbanks, Alaska site. Photo Source: Alaska Department of Environmental Conservation Photo Gallery

USGS scientists partnered with the Alaska Department of Environmental Conservation to investigate the potential for the natural attenuation of chlorinated ethenes in the cold environment of a contamination site in Fairbanks, Alaska. The Alaska Department of Transportation and Public Facilities Peger Road Operations and Maintenance Facility, Fairbanks, Alaska, has ground water contaminated with trichloroethene (TCE), benzene, and petroleum hydrocarbons. USGS scientists conducted a series of microcosm experiments to assess:

  • The microbial dechlorination of TCE, cis-dichloroethene (cis-DCE), and vinyl chloride (VC) in sediments from the Peger Road site.
  • The rates of chloroethene biodegradation under low temperature conditions (4°C) common in ground water at the Peger Road site.
  • The effectiveness of three electron donor amendments (molasses, shrimp and crab chitin, and "Hydrogen Release Compound") on the microbial degradation of TCE.
  • The potential significance at the site of chloroethene biodegradation processes other than reductive dechlorination.

The results of the experiments and associated field studies documented that:

  • Biodegradation can be a significant mechanism contributing to the natural attenuation of contaminants or for the in-situ bioremediation of contaminants even in very cold ground-water temperatures (4°C).
  • Natural attenuation assessments based only on the accumulation of reduced daughter products may significantly underestimate the potential for DCE and VC biodegradation because CO 2 was the sole product of cis-DCE and VC biodegradation at the Peger Road site.
  • Adding the electron donors HRC and molasses did not stimulate the reductive dechlorination of TCE; however, the addition of HRC and molasses did stimulate microbial degradation under manganese and iron (Mn/Fe) reducing conditions. This result suggests that addition of these electron donors favored microbial Mn/Fe-reduction to the detriment of microbial TCE dechlorinating activity.
  • In contrast, sediment microcosms where shrimp and crab chitin were added resulted in the establishment of mixed Mn/Fe reducing, sulfate (SO 4) reducing, and methanogenic conditions, and in enhanced rates of TCE biodegradation in two of three Peger Road sediments.

Water-quality monitoring data from the Peger Road site are being used to evaluate the ability of the Natural Attenuation Software (NAS) package to estimate cleanup times associated with combining the remediation of a contaminant source-area with using Monitored Natural Attenuation (MNA) to remediate the remaining downgradient contaminant plume. This site is one of eight demonstration sites that make up a diverse set of geologic, hydraulic, and geochemical environments. The evaluation is being conducted by the U.S. Navy, Virginia Polytechnic Institute and State University (Virginia Tech), and U.S. Geological Survey (USGS), with funding from the Environmental Security Technology Certification Program (ESTCP).

More Information
  • Paul M. Bradley, USGS,
  • Francis H. Chapelle, USGS,
Links Natural Attenuation Software (NAS) Information

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