Case Studies - MD003 - EVO injection within a fractured rock aquifer

Silver Springs, MD

At the former Naval Surface Warfare Center (NSWC) at White Oak, Silver Spring, Maryland, Pneumatic Fracturing (PF) was utilized to enhance reductive dechlorination of tetrachloroethene (PCE) within a tight fractured bedrock aquifer. The field-scale remedial action involved hot spot bioremediation of groundwater to permanently reduce contaminant levels to less than the Media Cleanup Standards.

Due to the low permeability of the aquifer matrix, PF was used to increase the subsurface permeability and to enhance the distribution of a vegetable oil substrate within the target treatment zone. Approximately 10,440 pounds of 60% oil substrate were injected into forty-five boreholes spaced within a 60,000 square foot treatment area. Five existing monitoring wells, located within 30 feet (ft) of the injection points, were used to monitor the distribution and persistence of the substrate and assess the treatment effectiveness of the injections. During both fracturing and substrate injection processes, pressure influence was observed in monitoring wells at distances exceeding 30 ft.

Based on field measurements and observations the following demonstrated the effectiveness of the delivery after pneumatic fracturing.

1. There was a significant increase in the total organic carbon in all the monitoring wells following the injections.
2. Vegetable oil emulsion was observed in the treatment zone monitoring wells.
3. Post-injection groundwater monitoring indicates significant increases in methane, soluble iron and soluble manganese concentrations in all the monitoring wells.
4. The groundwater sampling within a nine-month period demonstrated a 97% reduction in PCE and TCE.
5. DCE increased during the first 6 months followed by a significant reduction at the 9 month sampling event.
6. Based on the results of the sampling the EPA has rescinded the Administrative Order.

Short term evidence of substrate distribution was confirmed through visual identification of the vegetable oil emulsion in monitoring well ground water samples and elevated total organic carbon (TOC).

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