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Pneumatic Fracturing for Reducing Geologic Heterogenieties - Unconsolidated / Geology

A common misconception about using Pneumatic Fracturing is that extensive and thick low permeability zones or lenses are required to justify the use of the process. However, ARS has found that the majority of our sites contain subsurface geology with both high and low permeability zones. A good example of this is described below.

Site Description: Large industrial facility: Santa Clara, California

Geology: A semi-permeable layer of sandy silt and silty clay overlaying a thick silty clay with very low permeability.

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

Fracture depth range: 3.5 to 13.5 feet below ground surface

Permeability: Subsequent to fracturing, the rate of air flow increased 3.5 times during extraction tests utilizing the entire borehole. More dramatic was the increase in permeability during the interval tests, where the permeability increased by as much as 510 times in the low permeability clay zones.

Mass Removal: The rate of TCE mass removal increased 600% during extraction tests conducted on the entire borehole. The greatest increases in the rate of mass removal were found in clay zones, where the contaminants were removed at a rate up to 46,000 times greater than the pre-fracture conditions. Figure 1 summarizes the contaminant mass removal data for the interval extraction tests on a logarithmic scale.

Comments: Pre-fracture extraction tests indicated that the upper zones of the formation were somewhat permeable, while the clay zones beginning at a depth of 9.5 feet displayed very low permeability, as shown in Figure 2. Application of Pneumatic Fracturing was able to increase the rate at which air could be extracted from both zones of the formation, with the most dramatic effects being observed in the clay zones. This resulted in a reduction in geologic hetrogenieties or "uniformizing" the subsurface.

 

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