- Program Areas
- Installation Energy and Water
- Environmental Restoration
- Munitions Response
- Resource Conservation and Resiliency
- Weapons Systems and Platforms
Development of a Quantitative Framework for Evaluating Natural Attenuation of 1,1,1-TCA, 1,1-DCA, 1,1-DCE, and 1,4-Dioxane in Groundwater
Anthony Danko | NAVFAC EXWC
The overarching objectives of this project are to:
- Modify the EPA’s BIOCHLOR model and develop decision matrices to analyze historical monitoring data to extract rate constants for natural degradation of 1,1,1-TCA, 1,1-DCA, 1,1-DCE, vinyl chloride, and 1,4-dioxane so that Remedial Project Managers (RPMs) can use the rate constants to support monitored natural attenuation (MNA) as a remedy. and;
- Validate existing DNA-based quantitative real-time polymerase chain reaction (qPCR) assays for organisms and enzymes involved in the biodegradation of 1,1,1-TCA, 1,1-DCA, 1,1-DCE, and 1,4-dioxane by comparing the density of gene copies to the rate constants for removal of the contaminants at field scale as extracted from monitoring data or the rate constants for 1,4-dioxane degradation as determined by the 14C assay.
The methodologies for this project are patterned after several ESTCP projects, including the decision matrix used to develop BioPIC, the 14C-labeled TCE assay used to confirm degradation of TCE, and qPCR analyses. To facilitate regulatory approval, the logic will be built around a “Lines of Evidence for MNA” approach. Rate constants will be extracted by calibrating computer models to field data. Empirical data and models will then be used to predict concentrations at a Point of Compliance (POC). If these concentrations are less than remediation goals, then MNA is plausible. If MNA is not plausible, then models such as Natural Attenuation Software (NAS) will be used to identify the source reduction necessary to ensure that concentrations at the POC are less than RGs.
DNA-based qPCR assays will be used to provide evidence for the presence of microbes that may have the capability to degrade 1,1,1-TCA, or 1,1-DCA, or may produce enzymes that degrade 1,1,1-TCA, 1,1-DCA, 1,1-DCE, or 1,4-dioxane. There is a qPCR marker forDehalobactersp. (DHB) that carries out the dechlorination of 1,1,1-TCA, 1,1-DCA and 1,2-DCA, and a marker for 1,1-DCA reductive dehalogenase (DCA). The qPCR biomarkers for direct biodegradation of 1,4-dioxane include dioxane monooxygenase (DXMO) and aldehyde dehydrogenase (ALDH). The qPCR markers for co-oxidation of 1,1,1-TCA, 1,1-DCA, 1,1-DCE, or 1,4-dioxane include soluble methane monooxygenase (sMMO), ring hydroxylating toluene monooxygenase (RMO and RDEG) and phenol hydroxlyase (PHE).
Regulators are familiar with natural degradation of 1,1,1-TCA, 1,1-DCA, 1,1-DCE, and VC. This is not the case for 1,4-dioxane. To provide an independent estimate of degradation rates for 1,4-dioxane, water samples from field sites will be incubated with 14C-labeled 1,4-dioxane. The extent of 1,4-dioxane degradation will be monitored as the accumulation of 14CO2 or other degradation products. Rate constants will be calculated from the extent of degradation as a function of time of incubation.
The lack of an approach for elucidating degradation pathways for 1,1,1-TCA, 1,1-DCA, 1,1-DCE and 1,4-dioxane results in unnecessary financial and environmental costs for the DoD because it makes obtaining approval for MNA difficult. Active remediation can result in undesirable secondary impacts to groundwater quality such as pH changes, dissolution of toxic metals, and formation of methane (a potent greenhouse gas). Application of the decision matrices and BioPIC-TCA/Dioxane likely will increase the number of sites where MNA is implemented. These decision matrices will include logic for evaluating/selecting remediation strategies based onA Guide to Selecting Remedies for Subsurface Releases of Chlorinated Solventsand NAS. This approach will reduce capital and O&M expenses, and will help minimize impacts associated with invasive remediation options. (Anticipated Project Completion - 2020)