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• viable along a portion of the point-of-compliance, construction of such a system would likely result in diverting at least as much groundwater around the wall as would pass through the "treatment gate" of the wall. These conditions greatly reduce the effectiveness of a "treatment wall" or funnel-gate system and, as a result, this technology is considered technically ineffective, and therefore not viable for treatment of the groundwater impacts identified at the CHSL. Phytoremediation: Not Viable — In this process, plants can be used to adsorb contaminants or to create environments conducive to the degradation of contaminants through natural biochemical processes. For example, organic constituents can be adsorbed by the vegetation and metabolized or otherwise degraded by contact with the plant root system (rhizosphere) (Matso, 1995). Once in contact with the plant roots, many organic molecules are subject to microbial degradation. This process of plant induced breakdown or adsorption of contaminants is called phytoremediation. Because most plant roots only extend through the top 7 feet of soil, and trees such as poplars and weeping willows can reach maximum depths of only about 30 feet (Nyer et al., 1996), phytoremediation can only be applied to near-surface contamination projects. The • use of this technology for treatment of chlorinated VOCs at the CHSL is considered not viable within most portions of the identified plume because the depth of the aquifer exceeds the rooting depth of most trees and shrubs that would be used for such treatment. In-Situ Vitrification (ISV): Not Viable — This process stabilizes and immobilizes immobilizes inorganic contaminants by heating the soil mass to high temperatures (1500 to 2000 degrees Celsius), thereby melting the soil within the unsaturated zone. When the soil cools it forms a glass and crystalline-vitrified barrier that encapsulates inorganic contaminants. In addition, as the soil is heated, organic compounds are volatilized and can be removed by a vapor extraction system similar to that used in air sparging applications. Considering the depth to groundwater within the identified at the site, this technology is considered not viable at the CHSL. 3.5.3 Ex-Situ Treatment Alternatives Ex-situ treatment alternatives rely on groundwater extraction combined with one or more treatment technologies to remove contaminants from the extracted groundwater. At the CHSL, treated water could be re-injected into the aquifer, or discharged to the ground or • surface water body. A groundwater extraction system is common to all ex-situ corrective Engineering Feasibility Study Geo-Lo9ic Page ■ 17 Corral Hollow Sanitary Landfill A S S O C I A T[S January 25,2013