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purging, gas samples were collected in stainless steel Summa canisters and sent to Atmospheric <br /> Analysis &Consulting, Inc. for analysis by EPA method TO-14A(Appendix I). <br /> Second Semester Results <br /> VOCs were detected in all soil gas samples (Table 5). The highest concentration of any VOC was <br /> found in SG-l. Freon 12 was most often reported with the highest concentration in a sample. The <br /> most VOCs (eighteen) were reported in SG-Tl. <br /> Methane was detected in four soil gas wells this semester. <br /> VOCs have been detected in soil gas since monitoring began in October 2003, but VOC impact to <br /> groundwater has not been detected at any well since February 2002. Lack of detection of VOCs in <br /> groundwater indicates that the presence of VOCs in the soil at these concentrations is a benign <br /> condition at this landfill. <br /> tSoil Gas Trench <br /> Methane continues to be detected in the soil gas trench. Methane content in the gas beneath the <br /> liner of Module 1 is presently between 14% and 37%. When Module 1 liner was first installed in <br /> 2003, the gas beneath the liner was found to vary between 0 and 2%. The HDPE liner was <br /> extended over Module "I" refuse in the fall of 2006. It is possible that placing a HDPE barrier <br /> over Module "I" refuse has trapped landfill gas beneath. <br /> GROUNDWATER DIRECTION AND FLOW RATE <br /> Groundwater elevations were measured in monitoring wells during the first and second quarters. <br /> Groundwater was determined to flow towards the southwest (Figures 3 and 4). The calculated <br /> average linear groundwater flow velocity in the first quarter was 120.2 feet per year based on a <br /> hydraulic gradient of 0.0036 foot per foot. The calculated average linear groundwater flow <br /> velocity in the second quarter was 127.04 feet per year based on a hydraulic gradient of <br /> 0.0037 foot per foot (Appendix G). <br /> STANDARD OBSERVATIONS <br /> Regular site inspections were performed during the first semester of 2009. Monthly standard <br /> observations have been summarized (Appendix H). The electronic signatures on the forms certify <br /> that all observations were performed and are accurate. <br /> RUN-OFF/RUN-ON FACILITIES <br /> The Foothill Sanitary Landfill utilizes several methods to control run-on and run-off. The natural <br /> topography of the area controls any run-on into the site. Also, the working area is a significant <br /> distance from the property boundary, so run-on from surrounding properties is minimal. <br /> To control run-off, a perimeter ditch along the north, west and east ends of the unit directs all <br /> storm water run-off into a sedimentation basin on the east side of the site. The rest of the run-off <br /> Foothill Sanitary Landfill 9 Department of Public Works/Solid Waste <br /> 1 Semester 2009 Groundwater Monitoring County of San Joaquin—July 31,2009 <br /> i <br />