VA001 – Pneumatic Fracturing
Former Dry Cleaning Facility – Northern Virginia
Pneumatic Fracturing (PF) was used to enhance the Dual Phase Extraction (DPE) operation as the remedial alternative at the site. The project was conducted as the first step to final remedial action in July of 1994. The contaminants in the area of concern were primarily PCE and TCE. Pneumatic Fracturing was used to increase formation transmissivity and vadose zone permeability in the impacted fractured siltstone and shale formation. The DPE system was subsequently installed at the site to remediate existing contamination from bedrock in the subsurface. The use of Pneumatic Fracturing prior to DPE enhanced air flow rates, vacuum influence, and the ability to increase total removal of the contaminants of concern.
ARS applied pneumatic injections between 15 and 30 ft. below surface grade in open rock wells. The outcome of the PF operation is summarized below.
Pneumatic Fracturing was demonstrated to effectively improve the hydraulic connection between the wells in the test area. Prior to application of Pneumatic Fracturing, only minimal (less than 0.2’) groundwater drawdown influence was observed at wells on site. Following Pneumatic Fracturing, the formation was effectively “dewatered” for effective vacuum influence.
Extraction of TCE vapors following Pneumatic Fracturing also showed a much higher rate of mass removal. The average rate of mass removal was over three times the peak rate of mass removal during the DPE pilot test before Pneumatic Fracturing. The greater rate of TCE mass removal reduced the full-scale remediation duration from ten years to two years.
The vacuum radius of influence increased from 11 ft. prior to application of Pneumatic Fracturing to between 15 and 40 ft. (influence varied according to strike and dip orientation). Vacuum influence became a predictable function of strike and dip rather than an unpredictable product of formation heterogeneities. The much greater radius of influence substantially reduced the number of wells required and significantly reduced installation costs.