A draft treatability testing protocol was developed in 1998 to determine if enhanced biological reductive dechlorination (EBRD) was appropriate for remediation of chlorinated solvents in groundwater. The objective of this project was to apply the protocol at four Department of Defense (DoD) sites to determine whether EBRD was a feasible technology for full-scale implementation. The draft protocol has been revised based on the results of this project.
The protocol is comprised of the following four steps: 1) review of existing site data, 2) site selection and evaluation, 3) microcosm testing, and 4) field testing. A review is conducted at each step of the protocol to determine the site applicability of EBRD. Site review and evaluation assesses whether appropriate microbial populations and geochemical conditions exist or could be produced in situ to support biological reduction of chloroethenes to ethene. Microcosm and field tests evaluate the effect of added electron donors on the EBRD process by measuring the molar conversion of trichloroethene (TCE) or tetrachloroethene (PCE) to an ethane end point.
The draft protocol was applied at DoD sites with different hydrogeologic characteristics and contaminant profiles, including Cape Canaveral Air Station, FL, Alameda Point, CA, Fort Lewis, WA, and Camp Lejeune, NC. Electron donors evaluated included yeast extract, lactate, butyrate, lactate/benzoate, propionic acid, and acetic acid. Differences were observed between microcosm and field test data. Nonetheless, butyrate resulted in the greatest contaminant reduction at three sites and lactate at the other site. In spite of the discrepancies, microcosm and field tests indicated that butyrate was the most efficient electron donor. The draft protocol was then revised to include the following three EBRD recommendations: 1) not applicable for the site, 2) microcosm testing, and 3) field testing. Estimated implementation costs for the revised protocol are $77,000 to $94,000 for the microcosm option and $84,000 to $111,000 for the field option.
The revised protocol enables a rapid and cost-effective determination of the site applicability of EBRD for addressing chloroethene contamination in groundwater. Contaminant depth has the greatest effect on cost, as deeper depths incur greater drilling, waste disposal, and labor costs. A potential challenge is regulatory acceptance of contaminant re-injection during the field test. (Project Completed - 2003)