Accelerated anaerobic bioremediation of a solvent source area using direct injection, dover AFB, Delaware

A solvent source area consisting primarily of tetrachloroethene (PCE) and trichloroethene (TCE) was located adjacent to the hazardous waste storage building (Site SS07) at Dover Air Force Base (DAFB), Delaware. The selected treatment for the site focuses on the source area using accelerated anaerobic biodegradation (AAB) by direct-push injection methods to distribute substrate and nutrients and natural attenuation for the downgradient dissolved plume. In March 2006, nearly 102,000 gallons (386,000 liters) of amended water (a mixture of water, sodium lactate, emulsified vegetable oil [EVO], and nutrients) were injected into 53 locations at multiple depths. Monitoring data indicate that aquifer conditions rapidly became more reducing and favorable to anaerobic biodegradation. Dissolved iron and methane concentrations increased and sulfate and dissolved oxygen (DO) levels declined. Increases in cis-1,2-dichloroethene (cis-1,2-DCE) and vinyl chloride (VC) concentrations were observed as early as three months after the injection, indicating parent contaminant degradation. Decreasing PCE and TCE concentrations and the detection of ethene in several wells provide further evidence that complete anaerobic degradation is occurring. These trends continue to be seen nine months after injection.