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Leachate ® Waste Discharge Requirements require monitoring leachate flow rate,pH, and Electrical Conductivity on a monthly basis (Table 5). Leachate volumetric data for several months indicates reasonable average flow rates. Leachate is returned to the refuse in accordance with the WDRs for this landfill. The landfill operator has constructed two infusion points ("dry wells") in the refuse to receive this leachate. Vadose Zone Soil Gas First Semester Results Vadose zone soil gasses are generally measured at soil gas wells approximately 400 feet from the edge of refuse,but not from perimeter migration monitoring wells at the property boundary. Soil gasses were sampled on January 28, 2013. 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 stainless steel Summa canisters and sent to Atmospheric Analysis &Consulting, Inc. for analysis by EPA method TO-15 (Appendix H). VOCs were detected in nine of the ten soil gas samples (Table 6). The highest concentration of any VOC was found in SG-1 which is approximately 100 feet from the edge of refuse. Freon 12 was most often reported with the highest concentration in a sample. The most VOCs (six)were reported in SG-03. The source of the VOCs in the vadose zone is likely the old unlined portion of the landfill. ® Methane was detected in one interior soil gas well this semester below the regulatory limit. Data from the perimeter migration monitoring wells indicates that the facility is compliant with Title 27 regulations for off- site migration. VOCs have been consistently detected in soil gas since monitoring began in October 2003;however,VOCs in groundwater is not indicated. The presence of VOCs in the soil at these concentrations is apparently not, in itself, a significant condition at this landfill. GROUNDWATER DIRECTION AND FLOW RATE Groundwater elevations were measured in monitoring wells during the first and second quarters. Groundwater was determined to flow towards the east-southeast(Figures 3 and 4). The calculated average linear groundwater flow velocity in the first quarter was 67.33 feet per year based on a hydraulic gradient of 0.002 foot per foot. The calculated average linear groundwater flow velocity in the second quarter was 61.21 feet per year based on a hydraulic gradient of 0.00 18 foot per foot(Appendix F). STANDARD OBSERVATIONS Regular site inspections were performed during the first semester of 2013. Monthly standard observations have been summarized(Appendix G). The electronic signatures on the forms certify that all observations were performed and are accurate. Foothill Sanitary Landfill 9 Department of Public Works/Solid Waste I"Semester 2013 Groundwater Monitoring County of San Joaquin—July 25,2013