Anaerobic Bioremediation-Based Alternative Groundwater Cleanup Goals for TCE Plume

摘要

At a manufacturing facility, rows of injection wells were used to gravity-feed 60% sodium lactate solution into the shallow sand aquifer in order to promote anaerobic bioremediation of chloroethenes. Concentrations of the major contaminant, trichloroethene (TCE), were as high as 20,000 μg/L, and bioremediation successfully treated them to less than 50 μg/L within 2.5 years. During biotreatment, intermediate daughter products cis-l,2-dichloroethene (cDCE) and vinyl chloride (VC) accumulated for approximately one year and then their concentrations began to decrease. The complete dechlorination daughter product, ethene, was generated steadily throughout the process. The site groundwater cleanup goals were set by the state of Connecticut as the drinking-water criteria, which were expected to be difficult to attain in the short term. A model of the plume behavior was developed from historical data. The model demonstrated that the chloroethenes attenuated naturally, although slowly, and their concentrations decreased with distance downgradient from the source. The model results were used to negotiate alternative on-site cleanup goals that were calculated to be protective of human health at downgradient off-site receptors. These higher cleanup standards were acceptable to the regulatory agency as the endpoint for active remediation and the start of monitored natural attenuation.