Monday, July 30, 2007 - 10:45 AM
S17
Applying bioremediation for chlorinated solvent DNAPL source areas
Kent S. Sorenson Jr., CDM Inc., 1331 17th Street, Suite 1200, Denver, CO 80202 and Tamzen W. Macbeth, North Wind, Inc., 1425 Higham St., Idaho Falls, ID 83402.
Research in the 1980s and 1990s demonstrated that complete anaerobic biological transformation of chlorinated ethenes to ethene was feasible, and that certain bacteria coupled these transformations to growth. Until the last few years, however, most practitioners considered bioremediation to be inappropriate for chlorinated solvent source areas in groundwater. Recently, many researchers have investigated the use of biodegradation for remediation of source areas. Two important conclusions from this work have been changing the bioremediation paradigm. The first is that high contaminant concentrations are not toxic to certain bacteria, especially Dehalococcoides spp., but actually create an ecological niche conducive to contaminant degradation. The second conclusion is that mass transfer of contaminants from nonaqueous phases (liquid or sorbed) to the aqueous phase is enhanced, thereby accelerating mass removal significantly. Laboratory studies have demonstrated increases in contaminant mass removal rates ranging from a factor of 2 to 6 or more. A recent field study at the Ft. Lewis Logistics Center examined the extent of enhanced mass transfer due to bioremediation in a TCE DNAPL source area. The study demonstrated that aqueous contaminant mass flux could be increased in the field as in the laboratory. In addition, downgradient contaminant concentrations were observed to decrease by approximately an order of magnitude relative to baseline conditions following bioremediation. While much work remains to understand the limitations of this technology, the best strategies for optimization, and the endpoints that can be achieved within a reasonable timeframe, bioremediation appears increasingly promising for DNAPL source areas.