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® No VOCs were reported at this well this quarter. VOCs were last detected in this well on April 23, 2004; these detections are believed to have been introduced during well construction, and do not indicate groundwater impact from the landfill. Surface water Surface water samples were last collected on January 27, 2011,but were not available this quarter. All concentrations of field parameters and constituents of concern were below established concentration limits where the limits could be determined. Unsaturated Zone Soil Pore Gas The Monitoring and Reporting program for the landfill requires semi-annual VOC testing by TO-15 analysis. Soil gas samples were last collected on August 6, 2012, and is included in this second quarter report. Before sampling,the concentration of major gasses(Methane, Carbon Dioxide, and Oxygen) and pressure were measured using a CES-LANDTEC GEMTm2000 portable gas detector. The GEMTm2000 was operated until a steady-state gas composition indicated that the well was purged and ready for sampling. Soil gas samples were collected in 1-liter Summa canisters and sent for VOC analysis by EPA method TO-15. The concentrations of major gasses were recorded during the third quarter 2012 TO-15 sampling event, and a sample was collected from the probe most likely to have the highest VOC concentration: the sample was taken from the probe with the highest methane content, but if methane was not detected, the sample was collected from the deepest probe. The probe selected in the first TO-15 sampling event conducted in 2006 has been used thereafter for this analysis. Methane concentrations were zero in all perimeter migration monitoring wells during this quarter. VOCs were detected in all seven soil gas wells during this third quarter monitoring event. The highest VOC concentration was found in well SG-6D (Appendix Q. No "upwind" air sample was taken. Concentrations of major gasses (Methane, Carbon Dioxide,and Oxygen) and pressure were measured using a CES-LANDTEC GEMTm2000 portable gas detector on August 6, 2012 (Table 4). Groundwater Direction and Flow Rate Shallow Aquifer Groundwater elevations at wells SB-1, MW-4, MW-5,MW-8, MW-9A, MW-10A, and MW-11A indicate that the groundwater flow gradient in the shallow perched aquifer is to the north(Figure 2 and Appendix G). The average groundwater velocity is calculated to be 11.16 ft/yr based on a gradient of 0.04 feet per foot. • Corral Hollow Sanitary Landfill 14 Department of Public Works/Solid Waste 3'd Quarter 2012 Groundwater Monitoring County of San Joaquin—October 30,2012