2003 Seattle Annual Meeting (November 2–5, 2003)

Paper No. 3
Presentation Time: 8:35 AM


MORRILL, Penny1, SEEPERSAD, David2, LACRAMPE-COULOUME, Georges3, EDWARDS, Elizabeth4, SLEEP, Brent5, MCMASTER, Michaye6 and SHERWOOD LOLLAR, Barbara3, (1)Dept of Geology, Univ of Toronto, 22 Russell Street, Toronto, ON M5S 3B1, (2)Dept. of Chemical Engineering and Applied Chemistry, Univ of Toronto, 200 College Street, Toronto, ON M5S 3E5, (3)Dept. of Geology, Univ of Toronto, 22 Russell St, Toronto, ON M5S 3B1, (4)Department of Chemical Engineering and Applied Chemistry, Univ of Toronto, Toronto, ON, (5)Dept. of Civil Engineering, Univ of Toronto, Toronto, ON, (6)Geosyntec Consultants, Guelph, ON, morrill@geology.utoronto.ca

Pure phase tetrachloroethene (PCE) was injected into a 2D model aquifer to evaluate biologically enhanced dissolution of PCE dense non-aqueous phase liquid (DNAPL). The model aquifer was biostimulated with electron donors and subsequently bioaugmented with a reductively dechlorinating microbial consortium, KB-1. Stable carbon isotope measurements were collected periodically to determine if isotopic fractionation of parent and daughter products close to a source zone could be used to confirm microbial reductive dechlorination at concentrations close to PCE saturation, and to determine the effects on DNAPL dissolution rates.

Compositional and isotopic results provide evidence for reductive dechlorination near the source zone at PCE concentrations greater than saturation. The isotopic composition of the parent compound (PCE) in a system with pure phase present remains largely unchanged (–30.0 +/- 0.5 permil) due to the rate of dissolution of isotopically non-fractionated DNAPL (controlled by groundwater flow rates) outweighing the production of isotopically fractionated PCE due to biodegradation. Hence close to the source zone, confirmation of reductive dechlorination is based primarily on the appearance of the less chlorinated breakdown products and isotopic signatures for those products consistent with biodegradation. The isotope values of trichloroethene (TCE) ranged from -28.8 to –25.0 permil, indicative of dechlorination of TCE to of 1,2-dichloroethene (cDCE). The isotope values of cDCE ranged from -30.8 to –22.8 permil while the isotope values of vinyl chloride (VC) ranged from -57.2 to –34.4 permil. In all cases cDCE and VC were more depleted in 13C than the parent product from which they were derived. Over time, all of the breakdown products of reductive dechlorination of PCE showed isotopic enrichments trends consistent with reductive dechlorination through to the final non-chlorinated product, ethene. Enhanced dissolution due to biodegradation of PCE was demonstrated in this study based on differences in total mass flux between the control model aquifer and bioaugmented model aquifer.