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Regardless of these operational limitations, expanding the landfill gas extraction system provides an opportunity to reduce the VOC loads at the CHSL, and is a viable alternative to reducing VOCs at the site. 3.5.2 In-Situ Treatment Systems The treatment technologies discussed below focus on mitigation of VOCs. Inorganic impacts have not been identified in the release areas at the CHSL. In-Situ Air Sparging & Vapor Extraction System (IAS/VES): Viable — This in-situ treatment technology involves injection or "sparging" of clean air (or oxygen) into the saturated zone. The aeration of contaminated groundwater results in volatilization (stripping) of the VOCs from water and migration of the resulting gas phase constituents to the vadose (unsaturated) zone. Air sparging commonly operates in conjunction with a soil vapor extraction system to actively remove organic vapors from the vadose zone in the immediate vicinity of the air sparge wells. Emission control is often required to adsorb or destroy the VOCs collected by the vapor extraction system. • Though limiting factors for this technology include locating effective capture zones and the requirement for large vapor extraction and air sparging well galleries in the Corcoran Clay, and large energy requirements to operate the system, air sparging with vapor extraction is considered a technically viable alternative for the CHSL. Intrinsic Remediation: Viable — Intrinsic remediation relies on reducing or eliminating groundwater impacts using the existing conditions of the aquifer, including dispersion, dilution, biodegradation, or adsorption. Over time, these natural processes reduce groundwater impacts. This process is now at work at the CHSL, providing reduction in VOC concentrations between wells at the point of compliance (MW-5 and MW-8) and the EMP wells (MW-9A, MW-10A, and MW-11A). These impacts at the site are relatively low and limited in area due to this process,this alternative is considered viable. Bio-Enhancement/Inoculation: Not Viable — Bio-enhancement is a biological, in-situ remediation process that uses nutrient and microbial enhancement to accelerate natural biological degradation of VOCs and other organic contaminants. The biodegradation process requires co-metabolites (food supplements) and/or nutrients (nitrogen, phosphorous, etc.) to promote the growth of indigenous microorganisms in groundwater. Oxygen, nitrogen or • methane gases may be introduced along with co-metabolites and nutrients to shift the groundwater environment to conditions that are more suitable for the biodegradation Engineering Feasibility Study Geo-1.og0c Page ■ 15 Corral Hollow Sanitary Landfill ASSOCIATES January 25,2013