The objective of this project is to document a technical basis for quantifying aerobic degradation processes for chlorinated volatile organic compounds (cVOC) and use the information to develop practical, implementable protocols that incorporate these processes into environmental management practices for contaminated sites. Data from multiple Department of Defense (DoD) sites will be synthesized using samples collected in unperturbed aerobic plumes and downgradient of various deployed source treatments (e.g., anaerobic bioremediation and biowalls) to provide quantitative information about enhancement potential and synergies between technologies.

This project will leverage the latest developments in molecular biological tools, chemical techniques, and simulation models to develop improved protocols for environmental management of aerobic cVOC plumes. The products will be optimized, based on a focused and applied research effort, so that only the most diagnostic and useful parameters are included in the final protocols. Specific technologies for evaluation and possible inclusion are:

• Molecular biological tools—Enzyme activity probes (EAP), quantitative PCR (qPCR) targeting key bacterial taxa and catabolic genes, and fluorescence in situ hybridization (FISH). Ongoing research related to method reproducibility and replicability, sample matrix, and data interpretation will be used to optimize these efforts.

• Geochemical and compound specific isotope analysis (CSIA)—pH, redox potential, major anions and cations, dissolved gases, and CSIA for both stable carbon and hydrogen.

• Supporting simulation models and measurements—Emerging flux estimation and monitoring methods, and modeling tools. In particular, the application of REMchlor, a model recently developed with support from the Environmental Protection Agency (EPA) and DoD, will be pursued. This model provides a simple, innovative, and powerful approach to simulate changing spatio-temporal conditions and to rapidly screen how existing or potential source treatment actions combine with natural attenuation to stabilize plumes and control flux. This type of synthesis will be a key to successfully relying on the relatively slow natural attenuation degradation rates in aerobic settings.

Developing technology-based and scientifically defensible products that can be practically applied to DoD groundwater plumes requires rigorous testing at multiple sites under diverse conditions using predefined metrics, assessing the relative performance and potential utility of the techniques, and combining the results into detailed, practical, and broadly usable tools (i.e., technical protocols and guidance). This project will consolidate and build on previous DoD (SERDP and ESTCP) efforts related to dense nonaqueous phase liquid (DNAPL) source zones and large dilute plumes and extend protocols for natural attenuation beyond the existing requirements for anaerobic conditions and the associated limitations.

Both DoD and the Department of Energy (DOE) face long-term challenges associated with large aerobic plumes of chlorinated solvents; DoD alone has identified approximately 3,000 cVOC plumes, many in aerobic settings. A default assumption of "no degradation in aerobic plumes" substantively requires that source treatments provide complete removal; conversely, a technically defensible process that provides attenuation mechanisms and rates in aerobic plumes will define and bound the requirements for source and primary plume treatment performance and facilitate transition to natural or enhanced attenuation. Successful development will be transformational and provide a basis for combining technologies and a pathway to closure for many large DoD plumes.