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groundwater impacts. Measures such as reducing the moisture flux through wastes to limit leachate and landfill gas generation reduce the potential for related impacts to groundwater. As discussed in the Phase II EMP (GLA, 2012), groundwater monitoring data suggest that VOC concentrations do not exceed the respective Maximum Contaminant Levels beyond the Point of Compliance, and dispersion alone will attenuate VOC concentrations to below practical quantitation limit concentrations levels within 1000 feet of the landfill. In addition, currently there are no users of groundwater or environmental receptors within one mile of the CHSL. These conditions suggest that intrinsic remediation is an effective mitigation strategy that could be used to manage VOC concentrations. EMP monitoring wells are located such that they would form the intrinsic remediation monitoring network (Figure 10). Each well is screened to intercept the shallow aquifer and are positioned to provide groundwater chemistry information at varying directions and distances from the landfill (Table 11A). Costs for this alternative are typically associated with installation, sampling, and maintenance of groundwater monitoring wells. Since three new offsite monitoring wells were constructed as part of the EMP, there is no capital cost associated with implementing this alternative aside from installing optional bladder pumps to facilitate sampling and negotiating this alternative with the regulatory agencies (Table 11B). Operations and maintenance costs are included on Table 11C, and are those associated with additional groundwater monitoring and reporting. 4.5 GROUNDWATER EXTRACTION WITH EX-SITU TREATMENT Considering the low hydraulic conductivity of the Corcoran Clay aquifer materials at the site and the low yields that are available from wells, the groundwater extraction and treatment methods are not likely to pull in contaminated groundwater from the far edges of the plume, but rather would form a hydraulic barrier that would inhibit future migration of contaminant groundwater past the point of compliance. 4.5.1 Systems Common to Both Ex-Situ Treatment Systems Groundwater Extraction System. Both of the ex-situ treatment systems that are considered herein have a common groundwater extraction system that is configured to contain VOC- impacted groundwater along the point of compliance between wells MW-8 and SB-1 (Figure 11). Pumped groundwater will be conveyed to an above-ground treatment system that is unique to each of the two remedial alternatives. Based on recent limited aquifer tests, it is assumed that the groundwater extraction wells will be positioned approximately 100-feet Engineering Feasibility Study Geo-I.og0c Page ■ 25 Corral Hollow Sanitary landfill ASSOCIATES January 25,2013