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recently-completed EMP suggest that landfill-related VOC impacts extend approximately <br /> 1000 feet to the north and west of the site, at concentrations far below State and Federal <br /> regulatory standards. Chlorinated aliphatic compounds are the dominant type of VOC <br /> detected, with dichlorodifluoromethane (DCDFM), TCFM, and PCE typically comprising the <br /> highest concentrations. <br /> As previously noted, a small portion of waste was discovered outside of the permitted <br /> closure area and extending into property owned by Caltrans,just north of the CHSL (refer to <br /> Figure 7). Based on the extent of refuse and the depth to groundwater in that area, it <br /> appears that this waste is directly above the saturated portion of the shallow aquifer. <br /> Table 2 <br /> Summary of Hydraulic Properties of the Corcoran Clay <br /> Parameter Units Corcoran Clay <br /> Depth to groundwater ft 17 to 83 <br /> Aquifer thickness ft 20(Average) <br /> Hydraulic Gradient ft/ft 0.02 to 0.05 <br /> Principal Groundwater Flow Direction NA SW to N/NE <br /> Porosity(estimated) % 0.02 to 0.25 <br /> Hydraulic Conductivity* ft/day 0.0059 to 0.0383(Avg.0.012) <br /> Transmissivity* ftz/day 0.118 to 0.766(Avg.0.44) <br /> Average Groundwater Velocity ft/day Avg.0.023 <br /> *Bail down and recovery test results <br /> 2.5.2 Fate and Transport Assessment for the Release Area <br /> Chlorinated aliphatic VOC concentrations are typically too low to support a meaningful <br /> numerical dispersion model. Isoconcentration contours of the cumulative VOC <br /> concentrations suggest that VOCs reduce to non-detectable levels within approximately <br /> 1000 feet of the landfill property (Figure 5). <br /> 2.6 PREVIOUS CORRECTIVE ACTIONS <br /> In 1995 the CHSL was formally closed using a prescriptive final cover system, and a landfill <br /> gas extraction and destruction system was installed at the site in 2001. The final cover and <br /> landfill gas extraction system function together to contain and remove landfill gas from the <br /> waste prism and reduce movement of gas to the aquifers below the site. Extracted gas is <br /> Engineering Feasibility Study Geo-Lo Page ■ 7 <br /> Corral Hollow Sanitary Landfill w s s o t i ATE sg <br /> January 25,2013 <br />