- Program Areas
- Energy and Water
- Environmental Restoration
- Munitions Response
- Resource Conservation and Climate Change
- Weapons Systems and Platforms
Use of Enzyme Probes for Estimation of Trichloroethene Degradation Rates and Acceptance of Monitored Natural Attenuation
Over the past decade, monitored natural attenuation (MNA) increasingly has become accepted as a remedial alternative for organic compounds dissolved in groundwater. Enzyme probes have the potential to be used as practical tools for quickly and conclusively determining the potential for biologically mediated degradation and accurately estimating degradation rates. The objective of this project is to demonstrate the relationship between enzyme activity probes and contaminant degradation rates. Specific objectives include: (1) determine the importance of natural attenuation mechanisms at two Department of Defense (DoD) sites by combining a suite of innovative techniques to provide a comprehensive assessment of active degradation mechanisms, and (2) determine a biological degradation rate for trichloroethene (TCE) based on laboratory microcosms and normalize this rate based on enzyme probe activity, such that a realistic rate for the field can be obtained for the chlorinated solvent-contaminated DoD sites.
MNA relies on natural processes such as dispersion and biological degradation to reduce contaminant concentrations to acceptable levels without human intervention. The natural attenuation mechanism that is the main focus of MNA regulatory documents to date is anaerobic reductive dechlorination (ARD). For many years at a number of sites, it was thought that ARD was the only viable mechanism for MNA. However, due to the large size and general aerobic conditions of many of the plumes where MNA would be a viable option and ARD is not feasible, other biological mechanisms have received a great deal of research interest in more recent years, including direct oxidative and cometabolic processes. The primary focus of this project is aerobic cometabolic processes. Microcosm studies will be performed on samples collected from TCE-contaminated aquifers and will combine enzyme activity probes specific for aerobic oxygenase enzymes, molecular techniques such as polymerase chain reaction (PCR) amplification and fluorescent in situ hybridization (FISH) to provide evidence in support of enzyme activity probes, and contaminant transformation measurements to determine the rates of TCE cometabolism. The project will provide a comprehensive assessment of active aerobic degradation mechanisms at each demonstration site, as well as an estimate of the rate of contaminant degradation.
The cost of selecting and implementing MNA is low in comparison to more active remedies; however, careful characterization and thorough monitoring are essential to ensure that sufficient attenuation will take place to comply with all regulatory requirements. By determining degradation rates for TCE, this project will document natural attenuation and assess the environmental significance of attenuation at each demonstration site. Specifically of interest in this project is aerobic TCE degradation. The results could significantly enhance and strengthen a natural attenuation argument as well as provide cost savings for a contaminated site. (Anticipated Project Completion - 2010)
Points of Contact
Dr. M. Hope Lee
Idaho National Laboratory
SERDP and ESTCP
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