Fracturing is a technology designed to increase the efficiency of removal and in-situ treatment techniques. It is primarily used in difficult soil conditions to enlarge existing fissures and introduce new fractures. The new fractures occur primarily in the horizontal direction, and they facilitate Soil Vapor Extraction (SVE) or methods that inject gases or fluids for Enhanced Bioremediation. Common soil fracturing technologies include blast-enhanced fracturing, pneumatic fracturing (PF), the LasagnaTM process, and hydrofracturing.
Pneumatic Fracturing (PF). In the PF process, wells are drilled in the contaminated zone. Small (0.6-meter or 2-foot) portions of the zone receive short bursts (about 20 seconds) of compressed air. This fractures a small radius surrounding each well. The process is repeated throughout the contaminated zone. These new passageways increase the effectiveness of in situ processes and enhance extraction efficiencies by increasing contact between contaminants adsorbed onto soil particles and the extraction system. This technology is used primarily to fracture silts, clays, shale, and bedrock.
Hydrofracturing. Hydrofracturing injects pressurized water into wells to increase the permeability of the soil matrix. The process creates fissures, which expand away from the wells. The fissures are filled with a porous slurry composed of sand and guar gum gel. The sand grains hold the fracture open while an enzyme additive breaks the guar gum down into a thinned fluid. The fluid is pumped from the fracture, leaving permeable subsurface channels. The hydraulic fracturing process is repeated at varying depths (typically 5 to 30 ft) creating a “stack” of sand-filled fractures. This technology is used primarily to fracture silts, clays, shale, and bedrock. Hydraulic fracturing is applicable to a complete range of contaminant groups with no particular target group.
LasagnaTM Process. LasagnaTM is an integrated, in-situ treatment and removal technology. It uses electroosmosis and electrokinetics to move contaminants and groundwater in treatment layers (hence, Lasagna) in the contaminated soil. Fracturing is used to create sorption/degradation zones horizontally in the subsurface soil. (See the technical description of Electrokinetics.)
Limitations and Concerns
Fracturing may open new pathways for the unwanted spread of contaminants.
The final location of new fractures is not controllable.
Pockets of low permeability may still remain after using this technology.
The technology should not be used in areas of high seismic activity.
Hydraulic fracturing is not suitable for disturbed soils or fill material.
Investigation of possible underground utilities, structures, or trapped free product is required.
Fracturing near existing wells may damage well casings and seals.
An Underground Injection Control Permit will likely be required.
Typically hydraulic fractures are installed at depths ranging from 5 to 60 ft below ground surface, although some applications have targeted deeper zones. At more shallow depths, fractures have a tendency to climb and vent to the surface.
Displacement of soil will accompany hydraulic fracturing. The effects of this displacement must be evaluated at each site. Creating a shallow fracture (6 to 8 feet deep, for example) in soil typically raises the ground by roughly 1 inch, radiating around the fracture for roughly 8 to 25 ft.
If hot-fluid recirculation is planned, off-gas containment and treatment, as well as subsurface dewatering (to remove water generated by steam injection or to lower the water table for SVE) should be considered.
Fracturing is applicable to the complete range of contaminant types. While it can be used in the saturated subsurface, it is primarily used to fracture soil and rock, including bedrock.
Technology Development Status
Fracturing is widely used in the petroleum and water-well construction industries. While commercially available, it is an innovative method for use in hazardous waste remediation. Pneumatic fracturing technology is currently available from only one vendor. It has been demonstrated in the field under EPA’s SITE program. Hydrofracturing is a pilot-scale technology
Other Resources and Demonstrations
See Hydraulic and Pneumatic Fracturing Demonstrated at U.S. Department of Energy Portsmouth Gaseous Diffusion Plant, Ohio, and Department of Defense and Commercial Sites, 1998. DOE/EM-0348.
See X-231A Demonstration of In-Situ Remediation of DNAPL Compounds in Low Permeability Media by Soil Fracturing with Thermally Enhanced Mass Recovery or Reactive Barrier Destruction, 1998. R.L. Siegrist, et al. ORNL/TM—13534, NTIS: DE98058134.