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® The overall shape of the PCE plume is relatively symmetrical from an apparent source located near the northern boundary of the landfill. The source location appears to be centered between well MW-5 (LFG probe GW-1) and well MW-8, and is likely a result of LFG contact with groundwater in the shallow aquifer. 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-1, 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. This interpretation is based on the review of data from only two monitoring events from the three off site wells. 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, because the landfill was closed over 16 years ago in 1996, and surrounding conditions, such as the construction of freeways, have not changed, it is likely that the VOC plume extent is relatively stable. Data from the off-site wells (MW-9A, MW-l0A and MW- 11 A)will indicate if the extent of the plume is changing with time. Deep Aquifer -6 own 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. MW-7(UP gradient): Concentrations of all the parameters analyzed were within established concentration limits this quarter except for Electrical Conductivity(Table 2). A comparison of general water quality parameters between MW-7 (up-gradient) and MW-6 (downgradient) indicates better water • quality downgradient of the landfill. This indicates that the landfill has no affect on the deep aquifer. Corral Hollow Sanitary Landfill 13 Department of Public Works/Solid Waste 3rd Quarter 2012 Groundwater Monitoring County of San Joaquin—October 30,2012