- Program Areas
- Energy and Water
- Environmental Restoration
- Munitions Response
- Resource Conservation and Climate Change
- Weapons Systems and Platforms
Designing, Assessing, and Demonstrating Sustainable Bioaugmentation for Treatment of DNAPL Sources in Fractured Bedrock
The overall objective of this project is to evaluate the use of bioaugmentation for treatment of residual dense nonaqueous phase liquid (DNAPL) sources in fractured bedrock. Additionally, this project will assess treatment impact on the dissolved downgradient plume and develop design parameters to optimize bioaugmentation sustainability. Specifically, this evaluation will consist of an assessment of the DNAPL architecture, DNAPL dechlorination and dissolution rates in DNAPL-containing fractures, distribution and growth of dechlorinating bacteria both within and downgradient of the DNAPL source area, impact on dissolved contaminant flux emanating from the DNAPL source, and electron donor demand during treatment. The relationship between incremental DNAPL mass removal and dissolved tetrachloroethene (PCE)/trichloroethene (TCE) concentrations also will be assessed, with the ultimate goal of demonstrating that bioaugmentation can facilitate a final monitored natural attenuation (MNA) remedy.
Bioaugmentation involves the subsurface delivery of bacteria, along with electron donor and nutrients, that are capable of completely dechlorinating PCE and TCE. For chlorinated ethenes, bioaugmentation typically involves the use of mixed anaerobic cultures that contain Dehalococcoides sp. (DHC), or closely related strains, that can reductively dechlorinate the chlorinated ethenes. Results from SERDP project ER-1554 have demonstrated that bioaugmentation has the potential to treat DNAPL sources in fractured bedrock. The primary efforts in this demonstration will be to identify the fractures that contain the residual DNAPL sources, quantify the mass of DNAPL in these fractures, deliver bioaugmentation amendments to these fractures, then quantify the rate of DNAPL mass removal and dechlorination that occurs within these zones. The resultant impact on the downgradient dissolved plume and flux also will be assessed. While similar techniques have been applied for residual DNAPL sources in overburden materials, this demonstration will provide a novel application of this approach for fractured bedrock. The DNAPL source area will be characterized using multiple techniques (coring, partitioning tracers) to determine architecture and source mass. Conductive fractures will be identified using down-hole logging techniques. Dissolved contaminant flux migrating through these conductive zones before, during, and after bioaugmentation treatment will be measured using flux meters and multilevel samplers installed to intercept water-bearing fractures within (and downgradient of) the DNAPL source zone. Use of the multilevel samplers also will facilitate the identification of DNAPL sources in specific fractured intervals during the partitioning tracer testing. After characterization is completed, bioaugmentation amendments will be distributed through the monitoring zone. Monitoring will be used to measure bioaugmentation effectiveness and DNAPL mass removal, as well as dissolved contaminant flux. Partitioning tracer testing will be performed intermittently and at the completion of the demonstration in order to determine a relationship between partial DNAPL mass removal and dissolved contaminant flux.
This project will provide the Department of Defense (DoD) and stakeholders with management tools to improve the evaluation and treatment of DNAPL sources in fractured bedrock. The demonstration will serve as a means to verify the effectiveness of bioaugmentation for DNAPL sources in bedrock, thereby providing a potentially cost-effective solution at many challenging DoD sites. In addition, by better understanding the relationship between DNAPL architecture and flux, improved estimates and decisions regarding remedial time frames, source longevity, the extent of dissolved plumes, and remedial technology selection can be made. (Anticipated Project Completion - 2015)
Points of Contact
Dr. Charles Schaefer
Shaw Environmental, Inc.
SERDP and ESTCP
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