Biologically Enhanced DNAPL Dissolution Kinetics within Bedrock Fractures: A Bench Scale Experimental Study

Bioremediation of dense non-aqueous phase liquid (DNAPL) within a fractured bedrock setting presents unique remedial challenges, especially in consideration of microbe transport and activity.  Little research exists that characterizes the fate of microbes within fractured settings, which makes implementing efficient bioremediation of DNAPL source zones in fractured media difficult.  This research explores the dissolution behavior of tetrachloroethylene (PCE) DNAPL in a bench-scale three-dimensional (3-D) sandstone fracture network in the presence of microbial degradation activity, using Dehalococcoides sp. (DHC).  Microbial kinetics, transport, and DNAPL dissolution will be considered as a function of (DHC) inoculation dosage.  Microbial reaction kinetics, deduced from effluent breakthrough curves, are compared to those of static batch studies.  In addition results from discrete fracture experiments will be compared to three-dimensional fracture network experiments in order to better understand and improve bioremediation efforts in fractured bedrock settings.  Preliminary results from discrete fracture experiments suggest that fracture properties, such as aperture size and variability, may play a critical role in microbial reaction kinetics, transport, and delivery.  Additionally, results show up to a five-fold enhancement of DNAPL dissolution.