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Pneumatic Fracturing for Reducing Geologic Heterogeneities - (Fractured Rock)

Within fractured rock environments, the extent and interconnectivity of the existing fractures will dictate the formation's "bulk" permeability or conductivity. As described in the project below, fracturing was not only able to expand and dialate primary fractures, but also interconnect secondary fracture networks.

Site Description: Medium-sized former industrial facility

Geology: Moderately fractured siltstone and shale. Vadose zone with perched water.

Contaminants: Primarily trichloroethylene (TCE) with other chlorinated solvents and benzene.

Fracture depth range: 9.0 to 16.4 feet below ground surface

Permeability Enhancement: The rate of extracted air flow increased 8 times with all monitoring wells sealed and 175 times with four monitoring wells open for passive inlet of atmospheric air.

Mass Removal: The rate of TCE mass removal increased 8 times with all monitoring wells sealed and 25 times with four monitoring wells open for passive inlet of atmospheric air.

Vacuum Radius of Influence: The effective vacuum radius of influence increased from 10 feet to 20 feet.

Conclusions: All tests were performed under the USEPA Superfund Innovative Technology Evaluation (SITE) program. Pressure data, collected at perimeter monitoring wells, and surface heave measurements, indicate fractures propagated radially outward to 35 feet. Borehole video profiling confirmed that permeability enhancements were for the most part due to dilation of existing fractures, although the creation of new fractures was observed.

Chemical analysis of the extracted air during the post-fracture tests showed high concentrations of organic compounds previously only detected in trace amounts prior to fracturing. This data supported claims that fractures intersected and provided access to new DNAPL pockets.

 

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