ABSTRACT: A pilot-study for treatment of trichloroethene (TCE) and dechlorination products, dichloroethene (DCE) and vinyl chloride (VC), is currently being conducted at a site near the Duluth International Airport. The study began in April 2000 with direct push injection of a polylactate ester (HRC) into the aquifer immediately upgradient of a former source area monitoring well. The goal of the pilot test is to indicate if TCE, DCE, and VC concentrations can be adequately attenuated to merit full-scale application of the polylactate ester. After six monitoring events over a nine-month period, TCE decreased from 400 μg/L to <2 μg/L, cis-1,2-DCE increased from 50 μg/L to 750 μg/L, and VC increased from 10 μg/L to 20 μg/L.
The objective in using the polylactate ester was to provide a slow release hydrogen source as an electron donor to bioattenuate chlorinated compounds at a site where environmental conditions were not sufficient for natural attenuation. This study serves to quantify this objective. With respect to TCE, the rate of transformation increased from a virtually imperceptible rate of transformation to a half-life of 26 days. Alternatively, daughter products DCE and VC have accumulated. Relatively slow transformation rates for DCE and VC may be responsible for continued increases in DCE and VC concentrations. The concentration of DCE increased to a greater extent than can be accounted for by transformation of the parent compound TCE, which may indicate that additional TCE desorption from soil has occurred. It is not known whether DCE and VC are dechlorinating further downgradient due to the absence of a downgradient monitoring well in close proximity to the test well. If complete dechlorination is limited under the conditions as created, then alternative remedial methods for the transformation of DCE and VC need to be evaluated.