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Demonstration Bulletin: Hydraulic Fracturing of Contaminated Soil
Citation:
Barkley*, N P. Demonstration Bulletin: Hydraulic Fracturing of Contaminated Soil. U.S. Environmental Protection Agency, Washington, DC, EPA/540/MR-93/505, 1993.
Impact/Purpose:
to inform the public
Description:
Hydraulic fracturing is a physical process that creates fractures in silty clay soil to enhance its permeability. The technology, developed by the Risk Reduction Engineering Laboratory (RREL) and the University of Cincinnati, creates sand-filled horizontal fractures up to 1 in. in thickness and 20 ft in radius. These fractures are placod at multiple depths ranging from 5 to 30 ft below ground surface (bgs) to enhance the efficiency of treatment technologies such as soil vapor extraction, in situ bioremediation, and pump-and-treat systems. The fracturing process begins by using a hydraulic jet to cut a disk-shaped notch extending 0.5 ft from the borehole wall. Water is injected into the notch until a critical pressure is reached and a fracture is formetd. A proppant composed of a granular material (sancl) and a viscous fluid (guar gum and water mixture) is then pumped into the fracture at a rate of 16 to 24 gal/min. After pumping, the sand holds the fracture open while an enzyme additive breaks down the viscous fluid. The process is repeated at greater depths to create a stack of sand-filled hydraulic fractures. The aboveground equipment includes a mixer, a slurry pump, and gel storage tanks. The mixer continuously blends guar gum gel, water, enzyme, and sand. The slurry pump is used to transfer this mixture to the fractured area. The fracture aperture can be estimated by measuring the ground uplift in the vicinity of the borehole. A Ground Elevation Measuring System (GEMS), which uses a laser and an array of sensors, was developed to measure uplift of the ground surface in real time during hydraulic fracturing.