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Chloroethene Biodegradation Potential, ADOT/PF Peger Road Maintenance Facility, Fairbanks, Alaska

By Paul M. Bradley and Francis H. Chapelle

U.S. GEOLOGICAL SURVEY
Open-File Report 2004-1428

pdf This report is available online in pdf format (456 KB): USGS OFR 2004-1428

ABSTRACT

A series of 14C-radiotracer-based microcosm experiments were conducted to assess: 1) the extent, rate and products of microbial dechlorination of trichloroethene (TCE), cis-dichloroethene (cis-DCE) and vinyl chloride (VC) in sediments at the Peger Road site; 2) the effect of three electron donor amendments (molasses, shrimp and crab chitin, and "Hydrogen Release Compound" (HRC)) on microbial degradation of TCE in three Peger Road sediments; and 3) the potential significance at the site of chloroethene biodegradation processes other than reductive dechlorination.

In these experiments, TCE biodegradation yielded the reduced products, DCE and VC, and the oxidation product CO 2. Biodegradation of DCE and VC involved stoichiometric oxidation to CO 2. Both laboratory microcosm study and field redox assessment results indicated that the predominant terminal electron accepting process in Peger Road plume sediments under anoxic conditions was Mn/Fe-reduction. The rates of chloroethene biodegradation observed in Peger Road sediment microcosms under low temperature conditions (4°C) were within the range of those observed in sediments from temperate (20°C) aquifer systems. This result confirmed that biodegradation can be a significant mechanism for in situ contaminant remediation even in cold temperature aquifers. The fact that CO2 was the sole product of cis-DCE and VC biodegradation detected in Peger Road sediments indicated that a natural attenuation assessment based on reduced daughter product accumulation may significantly underestimate the potential for DCE and VC biodegradation at the Peger Road.

Neither HRC nor molasses addition stimulated TCE reductive dechlorination. The fact that molasses and HRC amendment did stimulate Mn/Fe-reduction suggests that addition of these electron donors favored microbial Mn/Fe-reduction to the detriment of microbial TCE dechlorinating activity. In contrast, amendment of sediment microcosms with shrimp and crab chitin resulted in the establishment of mixed Mn/Fe-reducing, SO42--reducing and methanogenic conditions and enhanced TCE biodegradation in two of three Peger Road sediment treatments.

CONTENTS

ABSTRACT
INTRODUCTION
MATERIAL AND METHODS
        Field Redox Assessment
        Radiochemicals
        Microcosm Studies
        Analytical Methods
RESULTS AND DISCUSSION
        Implications of In Situ Redox Conditions
        Dechlorination Rate Study
        Electron Donor Amendment Study
LITERATURE CITED
APPENDIX A
APPENDIX B

REPORT AVAILABILITY

pdf This report is available online in pdf format (456 KB): USGS OFR 2004-1428
To view the PDF document, you need the Adobe Acrobat® Reader installed on your computer. (A free copy of the Acrobat® Reader may be downloaded from Adobe Systems Incorporated.)

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