Assessment of Intrinsic Bioremediation at a PCE Contaminated Site

by Rectanus, Heather Veith

Abstract (Summary)
Groundwater parameter analysis, microcosm experiments, and microcosms modeling were undertaken to assess the potential of Monitored Natural Attenuation as a remediation strategy at Site 12 at the Naval Amphibious Base (NAB) Little Creek. Site 12 was contaminated with PCE waste disposed by a former dry cleaning facility. In the groundwater analysis, contaminant characteristics and redox indicators were evaluated to assess the reductive dechlorination potential of Site 12. The results of the groundwater analysis indicated that Site 12 exhibited sulfate-reducing and methanogenic conditions which provide the required environment for reductive dechlorination. However, Site 12 only demonstrated partial reductive dechlorination to cis-1,2-DCE and possible anaerobic oxidation of cis-1,2-DCE and VC to CO_{2}. Microcosms were designed to further evaluate the extent of microbial degradation of the chlorinated ethenes at Site 12 and to provide concentration versus time data for the estimation of chlorinated ethenes' biodegradation rates. The extent of degradation in the microcosms was consistent with the groundwater data. However, ethene production was not observed and the quantity of TCE measured for two of the microcosms differed substantially when compared to the groundwater data. The microcosm model used SEAM3D to simulate the results of the microcosm experiments (concentration versus time data) to estimate the biodegradation rates of PCE and its daughter products. The SEAM3D reductive dechlorination package, based on Monod kinetics, predicted for the MLS12-Shallow microcosm maximum specific utilization rates for PCE, TCE, cis-1,2-DCE and VC at 0.4, 0.42, 0.05, and 0.25 day^{-1}, respectively and half saturation coefficients for PCE, TCE, cis-1,2-DCE and VC at 0.41, 0.01, 0.07, and 0.02 mg/L, respectively. The results of this study suggest that while the groundwater environment provides the necessary conditions for reductive dechlorination, Site 12 is not an efficient system for reductive dechlorination. This lack of efficiency may stem from sparse microbial populations capable of reducing cis-1,2-DCE or the system may contain levels of PCE which inhibit the further reduction of cis-1,2-DCE. Based on the observed inhibitory relationship between PCE and cis-1,2-DCE and VC production, source removal would reduce the PCE levels and encourage further reductive dechlorination at Site 12. Therefore, the recommended first step for a monitered natural attenuation-based remediation strategy at Site 12 should be source removal.
Bibliographical Information:

Advisor:Duane Berry; Mark Widdowson; John Novak

School:Virginia Polytechnic Institute and State University

School Location:USA - Virginia

Source Type:Master's Thesis

Keywords:civil engineering


Date of Publication:10/12/2000

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