Electrokinetically-Enhanced Emplacement of Lactate in a Chlorinated Solvent Contaminated Clay Site to Promote Bioremediation

Bioremediation through the injection of electron donors and bacterial cultures is effective at treating chlorinated solvent contamination. However, it has had limited application in low permeability zones where amendments cannot be delivered successfully. This field-scale study investigated the application of electrokinetics to enhance the delivery of lactate at a clay site contaminated with chlorinated solvents. Groundwater and soil samples were collected before, during and for one year after the 71-day field test and analyzed for a wide suite of chemical and biological parameters. Lactate was successfully delivered to all monitoring locations. Electromigration transport rate was a minimum of 3.8 cm/day in zones with no observed advective transport during injection. Lactate emplacement resulted in the stimulation of bacterial populations, specifically within the phylum Firmicutes, which contains fermenters and strict anaerobes. This likely led to biodegradation, as the field trial resulted in significant decreases in both soil and aqueous phase chlorinated solvent concentrations. Contaminant decreases were also partially attributable to dilution, given evidence of some advective lactate flux. This research provides evidence that electrokinetically-enhanced bioremediation has potential as a treatment strategy for contaminated low permeability strata.