ANAEROBIC BIODEGRADATION OF TCE IN LABORATORY COLUMNS OF FRACTURED SAPROLITE

An investigation was conducted to determine if biodegradation of trichloroethylene (TCE) can occur in previously uncontaminated saturated fractured saprolite (highly weathered material derived from sedimentary rocks). Three undisturbed columns (~0.23 m diameter by 0.25 m long) of fractured saprolite were collected from approximately 2 m depth at an uncontaminated site on the Oak Ridge Reservation, Oak Ridge, TN. Ground water containing dissolved phase TCE under anaerobic condition was continuously pumped through all three columns. The first column was spiked with 1.0 ppm TCE, a second column was spiked with various concentrations of TCE (0.1 to 13 ppm), while a third column was inhibited of microbial activity. Indication of biodegradation occurred in both the 1 ppm column and the various concentration column while none in the inhibited column. Evidence of biodegradation included decreasing concentration of TCE in the effluent, appearance of daughter products (cDCE and VC), development of iron and then sulfate reducing conditions, and the detection of iron and sulfate reducing bacteria. A clonal library after exposure to high concentration of TCE (13 ppm) indicated the dominant microorganisms to be Geobacter, Geothrix, and Trichlorobacter. Therefore TCE biodegradation in saprolite can occur without amendments to enhance biodegradation, suggesting that monitored natural attenuation might be an acceptable strategy for remediation of TCE in ground water in fractured saprolite. The relatively rapid appearance of indicators of TCE dechlorination also suggest that these processes may occur even in shallow settings, which are typically subject to large seasonal changes in water table elevation and redox conditions.