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® • The PCE concentration detected at MW-11A(0.23 ug/L) is slightly above the laboratory method detection limit of 0.13 ug/L • A linear extrapolation of the 1 ug/L contour interval lines between a PCE concentration of 5.2 ug/L at MW-5 and a PCE concentration of 0.52 ug/L at MW-10A The overall shape of the PCE plume is relatively symmetrical from an apparent source located near the northern boundary of the landfill, an area that includes both County and Caltrans refuse. The source location appears to be centered between well MW-5, LFG probe GW-I, and well MW-8. The apparent western edge of VOC impacted groundwater adjacent to the landfill is the western edge of the Corcoran Clay Formation, (Figures 2 and 5). The apparent eastern edge of VOC impacted groundwater adjacent to the landfill is well SB-I, which is an apparent groundwater high elevation point in the shallow aquifer(Figure 2). The plume of impacted groundwater is elongated in the direction of groundwater flow, which is generally to the north- northeast from the landfill. A more definitive interpretation can be made after at least four monitoring events collected through at least one complete climatic cycle. The minimum amount of data for a rudimentary calculation of average VOC concentrations within the plume is also four data points. Whether the plume is increasing or decreasing cannot be determined from the limited data available. However, concentration of VOCs at the two impacted wells on site have been stable or decreasing since the installation of the LFG collection system in 2001, allowing the presumption that the plume has remained constant during that time. Data from the off-site wells (MW-9A, MW-I OA and MW-I IA) will indicate if the extent of the plume is changing with time. Deep Aquifer MW-6(Down gradient): Concentrations of all parameters were within established concentration limits where the limits could be determined (Table 2). Based on output from the Sanitas statistical software, an increasing trend is reported in the concentration of TDS and a decreasing trend is reported in the concentration of chloride this quarter(Table 3). However, the changes in concentration are very small. Report of a"trend"by Sanitas software is an artifact of the software. No VOCs were reported at this well this quarter. Other than false positives, no VOCs have been reported since Toluene was reported in 2005 when the well was first installed. These Toluene data indicate that this compound was probably introduced by the drilling company when this well was installed in 2003, but quickly reduced to "trace" in three quarters. Excluding probable contamination during well construction and compounds also found the QC blanks,no VOC has been reported in this well. Therefore,there has been no indication of impact from the landfill at this well. Corral Hollow Sanitary Landfill 13 Department of Public Works/Solid Waste 0 Quarter and Annual 2012 Groundwater Monitoring County of San Joaquin—January 15,2013