Subsurface treatment technologies

For practitioners of in situ technologies, note that U.S. EPA has issued a policy statement that reinjection of contaminated groundwater is allowed under Resource Conservation and Recovery Act (RCRA)35 36 as long as certain conditions are met. This policy is intended to apply to remedies involving in situ bioremediation and other forms of in situ treatment. Under this policy, groundwater may be reinjected if it is treated aboveground prior to reinjection. Treatment may be by a pump-and-treat system or by the addition of amendments meant to facilitate subsurface treatment. Also, the treatment must be intended to substantially reduce hazardous constituents in the groundwater (either before or after reinjection) the cleanup must be protective of human health and the environment and the injection must be part of a response action intended to clean up the environment.37... 

One category of the vadose zone treatment technologies which has been apphed in relatively numerous instances is soil vapor extraction (SVE) (with or without the introduction of air) (Hutzler et ai, 1989 Johnson et ai, 1990, 1994). The most effective apphcations of SVE employ careful control of apphed vacumn through designed extraction points about which are arrayed air introduction points to ensure airflow through the most contaminated zones. Figure 6a shows a typical SVE process diagram (NRC, 1994). Success with SVE methods has been more difficult to achieve where toxic nonvolatile compoimds are present in the source, or where permeabihty of the subsurface limits the zone influence of gas flow. 

An innovative technology called the "lasagna" process is based on the electrokinetic phenomenon called electro osmosis. The lasagna process was created to treat difficult wastes in low permeabiUty, sdt- and clay-laden soils (40). The lasagna process is so named because it consists of a number of layered subsurface electrodes and treatment zones. These layers can be constmcted either horizontally where contaminants are forced to more upward or in vertical position where lateral contaminant movement is desired. 

U.S. Environmoital Protection Agency, Subsurface Flow Constructed Wetlands for Wastewater Treatment A Technology Assessment, Report EPA/ 832-R/93/001. Washington, D.C, 1994. 

Soil auguring can be applied to a wide variety of sites, including wood treatment facilities, oil and gas production units, bulk storage sites, pipeline, manufactured gas plants and other sites contaminated with residual oils, petroleum products, VOCs, semi-VOCs, and other contaminants. This technology is also applicable to sites with complicated, heterogeneous subsurface geology that can render more traditional approaches ineffective, or at sites where excavation is not cost-effective or practical. 

The Biocube aerobic biofilter is an ex situ off-gas filtration system that is commercially available. The technology utilizes microbes to biologically oxidize volatile organic compounds (VOCs) and complex odors. It can be used in conjunction with vapor-vacuum-extraction (VVE), a process that draws gases from subsurface soil. These gases often require further treatment before being released into the atmosphere. Biocube has been field tested and has been implemented at over 100 sites for the treatment of hydrocarbon vapors. The technology has also been successfully used for odor control at a variety of sites. In addition, the Biocube system can treat odor and VOC emissions simultaneously. The units are modular, so additional stacks can be added as needed for increased flow and/or removal rates. 

The ARS Technologies, Inc., Ferox process is an in situ remediation technology for the treatment of chlorinated hydrocarbons, leachable heavy metals, and other contaminants. The process involves the subsurface injection and dispersion of reactive zero-valence iron powder into the saturated or unsaturated zones of a contaminated area. ARS Technologies claims that Ferox is applicable for treating the following chemicals trichloroethene (TCE), 1,1,1-trichloroethane (TCA), carbon tetrachloride, 1,1,2,2-tetrachloroethane, lindane, aromatic azo compounds, 1,2,3-trichloropropane, tetrachloroethene (PCE), nitro aromatic compounds, 1,2-dichloroethene (DCE), vinyl chloride, 4-chlorophenol, hexachloroethane, tribromomethane, ethylene dibromide (EDB), polychlorinated biphenyls (PCBs), Freon-113, unexploded ordinances (UXO), and soluble metals (copper, nickel, lead, cadmium, arsenic, and chromium). 

The Ecolotree buffer uses phytoremediation, or plant processes, for environmental remediation purposes. Ecolotree buffers can be used to reduce the migration of subsurface water and surface runoff, while also acting as an in situ remediation technique for both organic and heavy-metal contaminants, including benzene, toluene, ethylbenzene, and xylene (BTEX) chlorinated solvents ammunition wastes and excess nutrients in soil or water. The technology is commercially available and has been used at landfill and waste treatment sites. 

Electrokinetics has been used to mobilize metals and dissolved contaminants to in situ treatment or recovery zones. Electrokinetic transport uses these mechanisms to move bacteria through the subsurface to the contaminated media. The technology can be used to treat organic contaminants that adsorb to aquifer soils including halogenated hydrocarbons and non-aqueous-phase liquids (NAPLs). 

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. 

IT Corporation offers techniques that use ozone to oxidize contaminants in the subsurface or in above-ground treatment cells. Ozonation can be used as a primary treatment step, as a pretreatment step prior to bioremediation, or as a polishing step after other technologies. Ozonation has been tested in the laboratory, in pilot-scale demonstrations, and in full-scale applications. Patent... 

This technology is able to remove soil contaminants without the need to excavate, retrieve, and perform ex situ treatment. Electrical heating can be used to heat soil and remove contaminants hundreds of feet underground. Also, heating soil improves subsurface conditions for biodegradation of residual contaminants. 

The Trench Bio-Sparge (TBS) system is an in situ technology for the treatment of groundwater contaminated with organic compounds. The system employs diversion walls to direct the contaminant plume to a subsurface trench reactor, where treatment is achieved by physical and/or biological means. The technology has been field tested at the pilot scale but is not yet commercially available. 

Hugh Russell and Guy Sewell of the U.S. Environmental Protection Agency have investigated the application of reductive anaerobic biological in situ treatment (RABIT) to subsurface contamination in partnership with the Departments of Energy and Defense. This technology is still undergoing development and is not commercially available. 

---