Subsurface barriers

Subsurface barriers, low-permeability cutoff walls or diversions below ground are used to contain, capture, or redirect groundwater flow. The most common method uses bentonite slurry... 

U.S. EPA, Permeable Reactive Subsurface Barriers for the Interception and Remediation of Chlorinated Hydrocarbon and Chromium (VI) Plumes in Ground Water, Technical Report EPA-600-F-97-008, U.S. EPA, Washington, 1997. 

U.S. Environmental Protection Agency (1998). Evaluation of engineered subsurface barriers at waste sites, EPA 542-R-98-005, Office of Solid Waste and Emergency Response, Washington, DC. 

Isolation/containment this method minimizes the lateral migration of pollutants by installing subsurface barriers, such as a clay layer, an organo-clay layer, or a plastic liner. 

Narasimhan B, Sri Ranjan R. (1999). Creation of a subsurface barrier to contaminant transport using electrical potential gradients. Presented at the ASAE/CSAE-SCGR Annual International Meeting, July 18-21,1999, Paper No. 992124. St. Joseph, Ml ASAE. 

SUBSURFACE BARRIER GROUNDWATER (LEACHATE) EXTRACTION WELL... 

U.S. Environmental Protection Agency, Eermeable reactive subsurface barriers for the interception and remediation of chlorinated hydrocarbon and chromium (VI) plumes in ground waterf Rep. No. EPA-600-f97-008 Washington, D. C., 1997. 

A full-scale cryogenic barrier was demonstrated for five months at a clean site in Oak Ridge, Tennessee [Scientific Ecology Group 1995]. Freeze pipes were installed in a double row, inclined at a 45 angle to establish an inverted vee-shaped subsurface barrier. The pipes were set on 2.5 m centers in each row, with rows 1.2 m apart. 

Grant SA 1997, Artificially Frozen Ground as a Subsurface Barrier Technology,in Barrier Technologies for Environmental Management, D-153, Natl Res Council, Natl Academy Press, Wash DC. 

Some further details are the following. Film nonideality may be allowed for [192]. There may be a chemical activation barrier to the transfer step from monolayer to subsurface solution and hence also for monolayer formation by adsorption from solution [294-296]. Dissolving rates may be determined with the use of the radioactive labeling technique of Section III-6A, although precautions are necessary [297]. 

The slope of the water solubiUty curves for fuels is about the same, and is constant over the 20—40°C temperature range. Each decrease of 1°C decreases water solubiUty about 3 ppm. The sensitivity of dissolved water to fuel temperature change is important. For example, the temperature of fuel generally drops as it is pumped iato an airport underground hydrant system because subsurface temperatures are about 10 °C lower than typical storage temperatures. This difference produces free water droplets, but these are removed by pumping fuel through a filter-coalescer and hydrophobic barrier before deUvery iato aircraft. 

Principal Option for Containment/ Recovery Excavation Vacuum extraction Temporary cap/cover Hydraulic modification No action Groundwater pumping Subsurface drains Hydraulic barriers Low permeability barriers No action Overflow/underflow containment (i.e. oil booms) Run off/run on control Diversion/collection No action Capping/ nsulation Operations modifications Gas collection/removal No action... 

Subsurface drains are essentially permeable barriers designed to intercept the groundwater flow. The water must be collected at a low point and pumped or drained by gravity to the treatment system (Figure 8). Subsurface drains can also be used to isolate a waste disposal area by intercepting the flow of uncontaminated groundwater before it enters into a contaminated site. 

The landfill liner, cover, and hydraulic barrier all belong to the subsurface pollutant engineered containment system. The liner is designed at the bottom of a landfill to contain downward leachate. The cover is designed at the top of a landfill to prevent precipitation from infiltrating into the landfill. The hydraulic barrier, or cutoff walls, is a vertical compacted earthen system to contain horizontal flow of plume. The ultimate purpose of these barriers is to isolate contaminants from the environment and, therefore, to protect the soil and groundwater from pollution originating in the landfill or polluted site. 

A permeable reactive barrier (PRB) is defined as an in situ method for remediating contaminated groundwater that combines a passive chemical or biological treatment zone with subsurface fluid flow management. Treatment media may include zero-valent iron, chelators, sorbents, and microbes to address a wide variety of groundwater contaminants, such as chlorinated solvents, other organics,... 

Nonadsorptive retention of contaminants can also be beneficial. For example, oil droplets in the subsurface are effective in developing a reactive layer or decreasing the permeability of a sandy porous medium. Coulibaly and Borden (2004) describe laboratory and field studies where edible oils were successfully injected into the subsurface, as part of an in-situ permeable reactive barrier. The oil used in the experiment was injected in the subsurface either as a nonaqueous phase liquid (NAPL) or as an oil-in-water emulsion. The oil-in-water emulsion can be distributed through sands without excessive pressure buildup, contrary to NAPL injection, which requires introduction to the subsurface by high pressure. 

EnviroWall is a barrier. It serves to isolate contaminants and must be combined with another technology to treat contaminants. According to the vendor, EnviroWaU barriers can be installed to a maximum depth of 50 ft. The presence of boulders in the subsurface will increase treatment costs. The long-term durability of the HDPE material is not known. The system is best suited to treat contaminated groundwater and leachate at depths up to 50 ft when the contaminated media is underlain by an aquitard or other impermeable layer. 

Table 1 shows the estimated installation costs of a funnel-and-gate system using the Envirowall barrier technology. The presence of boulders in the subsurface will increase installation costs (D18981F, p. 22). 

After hydrogeological, chemical, and biological analysis of the subsurface is complete and parameters are known, a network of plastic tubing is injected in the contaminated plume and microbes are injected to destroy the contaminants. An impermeable vertical barrier or lining is installed with a vibratory hammer and insertion plate to maintain hydrogeologic control. The technology is capable of reaching depths of up to 100 ft. 

The cost of GSE Curtain Wall technology varies depending on site conditions. The cost of the HOPE ranges from 10 to 30/ft (D18980E, p. 17). According to the U.S. DOE, the cost of a synthetic barrier installation depends on the subsurface composition, depth, and method of installation. The DOE estimates that installation costs range from 20 to 250/m (D17096R, p. 2). 

The polywall barrier system was developed by Horizontal Technologies, Inc. (HTI), of Mat-lacha, Florida. The first polywall barrier system was completed in 1993. Since that time, the technology has been demonstrated at more than 10 other sites and used in full-scale remediation applications. The polywall barrier technology is currently commercially available through Horizontal Subsurface Systems, Inc. 

---