Natural Attenuation of Trichloroethylene in Rhizosphere Soils at the Savannah River Site: Fid-Bau Portal

Natural Attenuation of Trichloroethylene in Rhizosphere Soils at the Savannah River Site

Brigmon, R. L. / Bell, N. C. / Freedman, D. L. / Berry, C. J.

Extensive trichloroethylene (TCE) groundwater contamination has resulted from discharges to a former seepage basin in the A/M Area at the Department of Energy's Savannah River Site. The direction of groundwater flow has been determined and a seep line where the contaminated groundwater is estimated to emerge as surface water has been identified in a region of the Southern Sector of the A/M Area. This study was undertaken to estimate the potential of four rhizosphere soils along the seep line to naturally attenuate TCE. Microcosms were setup to evaluate both biotic and abiotic attenuation of TCE. Results demonstrated that sorption to soil was the dominant mechanism during the first week of incubation, with as much as 90% of the TCE removed from the aqueous phase. Linear partitioning coefficients (K_d) ranged from 0.83 to 7.4 mL/g, while organic carbon partition coefficients (K_oc) ranged from 72 to 180 mL/gC. Diffu-sional losses from the microcosms appeared to be a dominant fate mechanism during the remainder of the experiment, as indicated by results from the water controls. A limited amount of TCE biodegradation was observed, and attempts to stimulate TCE biodegradation by either methanotrophic or methanogenic activity through amendments with methane, oxygen, and methanol were unsuccessful. The appearance of cis-1,2-dichloroethylene (c-DCE), and trans-1,2-dichloroethylene (t-DCE) confirmed the potential for anaerobic reductive dechlorination. However, these daughter products represented less than 5% of the initial TCE added. The sorption results indicate that natural attenuation may represent a viable remediation option for the TCE plume as it passes through the rhizosphere.