Hydraulic fracturing (also known as emplacement) involves the use of high-pressure injection of water or remediation amendment to initiate new fractures in finer-grained soils and weathered bedrock. Following the fracture, amendments are then pumped into these zones. Typically, solid slurry chemistries like zero valent iron (ZVI), calcium peroxide, granular activated carbon or potassium persulfate are applied. Unlike pneumatic fracturing, hydraulic can be implemented through direct push drilling technology.
By exceeding the fracture pressure of the formation, new fractures are created in fine grained soils. Typically, two to five-foot zones are targeted with focused injection nozzles. Once the fractures have been created, amendments are injected into them to begin treatment of contaminants.
We use the vertical hydraulic fracturing method (also known as vertical inclusion propagation or VIP) for both single and multi-azimuth installations in addition to horizontal fracture emplacement.
Single-azimuth VIP is the trenchless PRB method, also known as the GeoSierra method. Instead of iron filings, sand or ceramic beads are injected creating a continuous conductive zone or permeable reactive treatment zone (PRTZ). The PRTZ is then used for injection of remedial amendments either by new injection wells installed within the PRTZ or via our specialized casings, which can be reused for injections. The objective of the design is a means for homogenous and continuous treatment which may be in a mid-plume location, as a cutoff treatment barrier, or for upgradient nitrate reduction prior to a downgradient PRB. The design considerations are endless.
The multi-azimuth approach was originally tested as an oil field well enhancement technology. It has been modified and adapted to allow installation in a variety of lithologic environments for source area remediation, as well as permeability enhancement for existing injection/extraction and potable water supply wells. Primarily used for injection of coarse high permeability sand, ceramic beads or other permeability enhancing materials like iron filings, injection field tests of a 6-wing configuration resulted in a 100x increase in permeability during enhancement of source area extraction wells. The multi-azimuth technology utilizes a similar vertical inclusion propagation technology to control injections in 4, 6 or 8 wing configurations. We have implemented the multi-azimuth VIP technology for enhancement of extraction wells, injection of iron filings in a source area, and for immediate and future injections for bioremediation.
The horizontal fracturing method is used to emplace proppants such as sands or ceramic beads or even oxidants when thin clay lenses exist, interception of vertical pathways or a greater lateral distribution is required, or treatment is required under a building. Temporary injection wells are typically installed using direct push technology and fractures are completed from the bottom up, depending on the project objectives and lithology. A horizontal notch is cut at the initiation depth followed by the injection of the highly viscous cross linked guar gum gel. An enzyme is added to the gel prior to injection so the gel’s starches biodegrade to sugars and water within a couple hours. Vertical spacing is typically two feet, and lateral inclusions may extend upwards of 50 feet in diameter.
Contaminants in fine grained soils and bedrock can only be effectively treated if the amendment achieves sufficient contact—and that can often only be achieved through fracturing the subsurface.