Geochemical and Microbiological Progress Metrics for Bioremediation of Mixed Chlorinated Ethenes & Methanes

This study demonstrates the design and benefits of using advanced geochemical and microbiological monitoring to evaluate bioremediation performance in a fractured rock environment. Bioaugmentation technology was applied to a commingled plume of chlorinated ethenes, primarily dissolved trichloroethene (TCE), and chlorinated methanes (carbon tetrachloride (CTC) and chloroform), in a fractured rock residual source area. Monitoring showed the notable effectiveness on CTC and chloroform, however understanding the challenges on remediating the commingled TCE and optimizing the design was the real value of advanced monitoring techniques.

To address the impacted bedrock aquifer that lacked naturally-occurring bacteria (no DHC), approximately 8,500 gallons of emulsified vegetable oil (EVO) augmented with SDC-9, a DHC-containing bacterial culture, was injected into a complex fracture network comprised of bedding plane and tectonic fractures. The goal of the advanced monitoring was to support the demonstration of the effectiveness of bioaugmentation as a potential remedy scalable to larger areas, but also to characterize the reasons for challenges that presented themselves and to optimize the design.

Bioaugmentation performance was evaluated and quantified using a 3D monitoring well network with analyses for both chemical and biological constituents. The parameters monitored included concentration trends of tracers, of chlorinated ethenes, ethanes, methanes and benzenes (including all daughter products), geochemical conditions (DO, ORP, pH, alkalinity, methane, ethane, ethene, sulfate, ferric and ferrous iron, manganese, TOC), biological conditions (Dehalococcoides (DHC) functional genes bvcA Reductase (BVC) and vcrA Reductase (VCR), functional gene tceA Reductase and dehalobacter (DHBt), and metabolic products of the organic substrate), and stable isotope changes (CSIA) in chlorinated ethene parent and daughter compounds. Seasonal influences were also recognized and given consideration in our evaluation. The results of our monitoring of progress metrics showed that enhanced biodegradation of chlorinated VOCs was successful in particular portions of the fracture network that were treated by injected amendments.