Enhanced in situ anaerobic bioremediation has emerged as a viable and cost-effective strategy for the remediation of chlorinated solvents in groundwater. The technology leads to complete mineralization of contaminants in situ with little impact on infrastructure, at a relatively low cost compared to more active, engineered remedial systems. Although the success of enhanced anaerobic bioremediation has not been universally demonstrated, it is clear that the technology holds great promise when properly applied. This project evaluated and compared alternative approaches to implementing enhanced bioremediation and produced a guidance document and cost-estimating tool to assist Department of Defense (DoD) remedial project managers (RPM) in assessing the application of this technology at their sites.

Technology Description

Enhanced in situ anaerobic bioremediation involves the delivery of electron donors into the subsurface for the purpose of stimulating microbial growth and development. The electron donors are generally organic compounds that are added to create anaerobic groundwater treatment zones and to generate hydrogen through fermentation reactions, thereby creating conditions conducive to the anaerobic biodegradation of chlorinated solvents dissolved in groundwater. One of the primary mechanisms for the breakdown of chlorinated solvents is anaerobic reductive dechlorination. In some cases, organisms may need to be added, either because the native microorganisms are not capable of performing all of the required transformations, or to reduce the time needed for acclimation of the native microbial populations. This project was executed using a three-phased approach, which included (1) collecting all available information on the state-of-the-art application of enhanced bioremediation technologies; (2) conducting a comparative analysis of the results; and (3) producing a cost-estimating tool and final report detailing the state-of-the-art and providing guidance for effective application of enhanced bioremediation.

Demonstration Results

The Phase I Site Survey report includes information regarding several alternative approaches for applying enhanced anaerobic dechlorination and compares the efficacy of these approaches under various site conditions. The survey included data from 93 sites, including information on the contaminants of concern; the type, cost, and effectiveness of the selected substrate; the type of impacted media; the application technique; the aggressiveness of treatment; any regulatory concerns; and the life cycle costs. The subsequent Principles and Practices of Enhanced Anaerobic Bioremediation of Chlorinated Solvents guidance document includes an overview of enhanced in situ anaerobic bioremediation, a description of the science and principles of anaerobic bioremediation, and the steps required to practice and evaluate the technology. Once it has been determined that enhanced bioremediation is suitable for application at a site, the document provides further guidance on the design of appropriate enhanced bioremediation system configurations and selection of appropriate substrates. A supplemental Microsoft Excel-based cost-estimating tool was developed to help screen various configurations of implementing enhanced bioremediation.

Implementation Issues

Through a tri-service effort involving the Naval Facilities Engineering Command, Air Force Center for Environmental Excellence, and U.S. Army Corps of Engineers, this project produced a guidance document that is intended to help DoD RPMs and their contractors determine whether enhanced bioremediation is appropriate for their sites and then identify the optimum approaches to achieve their remedial goals. The document can help RPMs make effective decisions that save time and money by providing a technology "road map" for appropriate and successful implementation of enhanced bioremediation, while identifying "red flags" that may limit success. (Project Completed - 2005)