Presentation Description
Project SABRE: Lab and Field Results of the Bioremediation of a TCE DNAPL Source Zone
Project SABRE (Source Area BioREmediation) is a public/private consortium of twelve companies, two government agencies, and three research institutions whose charter is to determine if enhanced anaerobic bioremediation can result in effective and quantifiable treatment of chlorinated solvent DNAPL source areas.  The results presented here represent laboratory studies, biological and geochemical process modelling, and field testing undertaken over four years as part of a $5.7 MM project designed to (a) demonstrate effective TCE DNAPL treatment via a combination of solubility enhancement and complete degradation and (b) provide detailed quantitative process understanding at the field scale. 

Laboratory studies included a large-scale microcosm study which demonstrated that emulsified vegetable oil (EVO) was an effective electron donor at promoting reductive dechlorination in the presence of elevated (e.g. 400-800 mg/L) concentrations of TCE.  Bioaugmentation and nutrient addition also enhanced the rate of TCE biodegradation.  This work was followed by a series of soil columns that contained TCE DNAPL or received high (e.g. 250-400 mg/L) levels of influent TCE in order to simulate conditions in or directly down gradient of the DNAPL source zone.  When EVO was added to columns, it was observed to partition into the DNAPL, creating a long-term source of electron donor.  Dechlorination in the presence of TCE DNAPL was variable and sometimes stopped at c-DCE.  Dechlorination in the presence of aqueous phase TCE concentration was more extensive, in some cases resulting in the complete dechlorination of TCE to ethene in the columns.  Simple and complex biological process models were largely effective at simulating the column results, lending insight to the key processes involved. 
 
The field work is being performed using an intensively monitored and controlled test cell containing TCE DNAPL A 3-sided sheet-pile test cell encloses a 30 m long, 4 m wide and 6.5 m deep section of contaminated aquifer.  Flow through the cell (residence time 45 days) is controlled by an extraction well located at the downgradient closed end.  The cell has been intensively monitored via a 450-point network.  Dechlorination activity occurring under controlled flow but unamended conditions was evaluated over a ~100 d baseline period prior to bioremediation. Effluent from the cell during the baseline period contained primarily cDCE (2500 uM) and TCE (1000 uM).  Total chlorinated ethenes in the effluent were ten times those present in the influent.   Baseline geochemical conditions were characterized by low dissolved oxygen, negative ORP, dissolved iron, and 400 – 800 mg/L sulfate. 

In May 2007, 2900 L of EVO was injected into the cell, followed two weeks later by bioaugmentation with a commercial consortium of dechlorinating bacteria.  EVO injection resulted in sustained TOC of 200 – 300 mg/L throughout the cell including the influent zone.   Following initiation of bioremediation, TCE was rapidly converted to cDCE throughout most of the test cell.   While cDCE remains the dominant chloroethene in the groundwater after more than one year of operation, concentrations of VC and ethene are significantly increasing over time.  Increases in chloride from ~ 300 to ~ 500 mg/L are further evidence of increased dechlorination. DNAPL dissolution is estimated to be ~2X over baseline values due to bioremediation, while a significant fraction of the original DNAPL appears to have been removed from the test cell, based upon initial DNAPL estimates.