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VOCs <br /> Two VOCs were detected at trace concentrations in MW-2R the July 2008 sampling event, but <br /> were not found in a subsequent confirmation sampling in August. Therefore, other than false <br /> positives, no VOCs were found in any wells this semester. No VOCs have been confirmed in any <br /> groundwater well at the Foothill Landfill since October 2001, over seven years ago. <br /> Surface Water <br /> Surface water samples were not available this semester. <br /> Leachate <br /> Waste Discharge Requirements require monitoring leachate flow rate, pH, and Electrical <br /> Conductivity on a monthly basis (Table 3). Leachate volumetric data for several months indicates <br /> reasonable average flow rates. <br /> Vadose Zone Soil Gas <br /> Soil gasses were sampled on July 29, 2008. Samples were collected by first measuring the <br /> methane content using a CES-LANDTEC GEMTM 500 portable gas analyzer. The GEMTM 500 <br /> was operated until a steady-state gas composition indicated that the well was purged. After <br /> 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 4). The highest concentration of any VOC was <br /> found in SG-6. Freon 12 was most often reported with the highest concentration in a sample. The <br /> most VOCs (twenty-two) were reported in SG-T1. <br /> Methane was not detected in any 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 /> GROUNDWATER DIRECTION AND FLOW RATE <br /> Groundwater elevations were measured in monitoring wells during the third and fourth quarters. <br /> Groundwater was determined to flow towards the southwest (Figures 3 and 4). The calculated <br /> average linear groundwater flow velocity in the third quarter was 134.66 feet per year based on a <br /> hydraulic gradient of 0.004 foot per foot. The calculated average linear groundwater flow velocity <br /> in the fourth quarter was 127.9 feet per year based on a hydraulic gradient of 0.0038 foot per foot <br /> (Appendix G). <br /> Foothill Sanitary Landfill $ Department of Public Works/Soli <br /> d Waste <br /> 2"d Semester and Annual 2008 Groundwater Monitoring County of San Joaquin—January 31,2009 <br />