ENHANCED REDUCTIVE DECHLORINATION OF PCE IN BEDROCK: PILOT TO FULL-SCALE

The results are presented for a pilot test demonstrating the enhanced reductive dechlorination of tetrachloroethene (PCE) in bedrock groundwater using an in-situ reactive zone (IRZ). The pilot test was implemented in the mid-portion of an approximately 3,000-foot long plume. Initial PCE groundwater concentrations were approximately 120 micrograms per liter (μg/L).Historical groundwater monitoring data indicated volatile organic concentrations (VOC) concentrations were in equilibrium throughout the plume, with little evidence of the degradation of PCE. Baseline biogeochemical sampling was performed, and the results indicated the environment in each area was aerobic to transitional. A review of the electron acceptor and donor analytical data indicated the rate of attenuation was also limited due to a lack of organic carbon (electron donor/substrate).A pilot test was initiated that consisted of an injection well and two downgradient monitoring wells. A reagent of molasses and water was injected on either a weekly or bi-weekly interval. The results of the pilot tests indicate anaerobic and reducing conditions were established and organic carbon concentrations increased in and downgradient of the injection wells. The increased amount of organic carbon coupled with the anaerobic and reducing conditions promoted the reductive dechlorination of PCE to lesser chlorinated compounds (TCE, DCE, VC, and ethene). The increased rate of attenuation decreased the ratio of PCE to daughter products, and reduced overall VOC mass within the pilot test areas. The results of the 15-month long pilot test were used to implement a full-scale in-situ treatment system for the site.