Technology Description

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.