Full-scale Enhanced Anaerobic Bioremediation of Two Low Permeability Source Areas

Enhanced anaerobic bioremediation through electron donor amendments in and directly downgradient of suspected source areas was used to treat trichloroethylene (TCE) found in two source areas at a manufacturing site.  The treatment system included the design and installation of a biobarrier in highly permeable channel fill surrounding the source areas and direct injections into lower permeability flood plain deposits containing the source material.  Two electron donors, emulsified vegetable oil (EVO) and EHC®, were employed to promote reductive dechlorination of TCE.  A total of 21,120 pounds of 60% EVO solution was delivered to the aquifer through a series of 55 injection wells screened across the zone of highest dissolved phase VOC concentrations to ensure a uniform distribution of amendment.  The biobarriers were emplaced prior to source treatment to allow for time for bioreactive zones to develop around the source areas to minimize the transport of contaminants liberated by the source treatment.

EHC® was selected for the flood plain deposits because it could be injected into the low permeability formation.  At total of 28,897 pounds of EHC® was injected into the two source areas under high (100-400 psia) pressure through 87 injection points.  The distribution of EHC^® in the subsurface was directly and quantitatively measured using confirmation soil cores and magnetic susceptibility measurements.  

Groundwater sampling completed three months post injection demonstrates that extensive reductive dechlorination is occurring in both source areas and at downgradient locations.  In several cases downgradient monitoring wells now contain predominantly ethene and ethane.