Biologically Enhanced Tetrachloroethene DNAPL Dissolution in An Experimental Fracture Network

Chlorinated solvents and DNAPLs are presently one of the more difficult among organic groundwater contaminants at remedial sites in the United States.  Unfortunately, many of these sites occur in fractured geologic media.  The complex nature of flow and transport through fractured systems combined with the prevalence and persistence of DNAPL contamination creates a unique remedial challenge.  This research seeks to better understand DNAPL dissolution kinetics during biodegradation in a three-dimensional experimental fractured aquifer.  Experiments are conducted using Dehalococcoides sp. (DHC) to reductively dechlorinate tetrachloroethene (PCE) enhancing the dissolution of pure phase DNAPL.  DNAPL dissolution in the presence of biological activity is compared to abiotic dissolution in order to establish the extent of enhancement due to DHC activity.  In addition to reaction kinetics, the transport and delivery of microbes is affected by complex flow characteristics of a fracture network.  This research also investigates the relative effects of matrix diffusion, dead-end fracture diffusion, and advective channeling on chemical and biological transport.  Additionally, the research investigates the relationship between fracture aperture variability and the extent of biological enhancement of dissolution.  Initial results show DNAPL dissolution enhancement factors as high as 30.