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0 Extent of Groundwater Impact Delineated The area of groundwater impact apparently extends northeast to a maximum distance of approximately 900 feet from the landfill property (Figure 5). The extent of groundwater impact is delineated based on the following evaluation of PCE concentration, as follows: • No PCE detected at MW -9A • The PCE concentrations detected at MW -10A (0.39 ug/L) and MW -11A (0.16 ug/L) are 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 4.2 ug/L at MW -5 and a PCE concentration of 0.39 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 -1, 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 -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. After the first seven monitoring events and one climatic cycle, the data may indicate a decreasing plume in the area of well 11-A. There does not appear to be trends in the VOC data for the other wells at this time. However, the concentration of VOCs at the two impacted wells on site have been relatively stable 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 -10A and MW -1 IA) will indicate if the extent of the plume is changing with respect to time. Deep Aquifer MW-6(Do wn gradient): Concentrations of all the parameters analyzed were within established concentration limits this quarter (Table 2). A "significantly increasing" trend is reported by the Sanitas program for TDS this quarter (Table 3). 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 Corral Hollow Sanitary Landfill 15 Department of Public Works/Solid Waste 4" Quarter and Annual 2013 Groundwater Monitoring County of San Joaquin — January 15, 2014