APPLICATION OF EDIBLE OILS (VOS™) IN THE VADOSE ZONE FOR SUSTAINABLE TREATMENT OF CVOCS BY REDUCTIVE DECHLORINATION

Chlorinated solvents (cVOCs) remain in lower permeability zones along an abandoned process sewer line at the Department of Energy’s Savannah River Site (SRS). Soil vapor extraction was not effective for these tight zones in the coastal plain sediments and the trapped solvents are a slow but continuous source of contamination primarily by gas diffusion. A low cost, sustainable means to sequester and remediate these slowly migrating contaminants in an aerobic vadose zone was needed. cVOCs are easily sequestered by partitioning into edible oils and reductive dechlorination can be established under the correct geochemical conditions. Based on successes of stimulating reductive dechlorination using carbon sources in groundwater systems and the sequestering ability of edible oils, a substrate was developed for the vadose zone. VOS™ (patent pending) is a thixotropic formulation of edible oil, water, nutrients, buffers and a Dehalococcoides strain that is easily injected into the vadose zone and then retains a high saturation to maintain reducing conditions.

A field pilot study is being conducted to evaluate the effectiveness and longevity of the VOS deployment to mitigate the cVOC contamination. In February 2010, approximately 230 gallons of VOS was injected into three injection points installed 30-35 ft deep beneath a tight zone with known PCE and TCE contamination. Twenty gas sample ports were installed in the injection zone and deeper into the vadose zone for evaluation. Samples are collected weekly and are analyzed for cVOCs and their breakdown products. Additional gas analyses include light hydrocarbons, carbon dioxide and oxygen. Soil cores are collected every six months for analysis of cVOCs and specific geochemical parameters.

A case study describing the injection of the VOS, gas and soil analytical results, effectiveness and expected longevity of the treatment will be presented.