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Vadose Zone Soil Gas Soil gasses were sampled on March 13, 2007. Samples were collected by first measuring the methane content using a CES-LANDTEC GEMTM 500 portable gas analyzer. The GEMTM 500 was operated until a steady-state gas composition indicated that the well was purged. After purging, gas samples were collected in 6-liter Summa canisters and sent to Atmospheric Analysis & Consulting, Inc. for analysis by EPA method TO-14A. First Semester Results VOCs were detected in all soil gas samples (Table 6). The highest concentration of any VOC was found in SG-l. Freon 12 was most often reported with the highest concentration in a sample. The most VOCs (ten) were reported in SG-10. ' 1 Methane concentrations were 0 percent in all the wells except for 0. percent in SG 1 and 10.8 percent in SG-11. Continuing detection of VOCs in soil gas since monitoring began in October 2003 with lack of impact by VOCs to groundwater at any well since February 2002 indicates that the presence of VOCs at these concentrations is a benign condition at this landfill. GROUNDWATER DIRECTION AND FLOW RATE Groundwater elevations were measured in monitoring wells MW-1, MW-2R, and MW-3 during the first and second quarters. Groundwater was determined to flow towards the southwest(Figures 3 and 4). The calculated average linear groundwater flow velocity in the first quarter was 63.96 feet per year based on a hydraulic gradient of 0.0019 foot per foot. The calculated average linear groundwater flow velocity in the 1 second quarter was 53.86 feet per year based on a hydraulic gradient of 0.0016 foot per foot. These calculations can be found in Appendix G. STANDARD OBSERVATIONS Regular site inspections were performed during the first semester of 2007. Monthly standard observations 1 have been summarized(Appendix H). The electronic signatures on the forms certify that all observations were performed and are accurate. RUN-OFF/RUN-ON FACILITIES The Foothill Sanitary Landfill utilizes several methods to control run-on and run-off. The natural topography of the area controls any run-on into the site. Also, the working area is a significant distance from the property boundary, so run-on from surrounding properties is minimal. ' To control run-off, a perimeter ditch along the north, west and east ends of the unit directs all storm water run-off into a sedimentation basin on the east side of the site. The rest of the run-off from the unit gathers into a sedimentation basin at the southeast corner of Module 1. There were no breeches to any of the run- on/run-off facilities during this monitoring period. Foothill Sanitary landfill 9 Department of Public Works/Solid Waste 1s'Semester Groundwater Monitoring County of San Joaquin—July 31,2007