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Storm Water There were no stormwater discharges from the site during this monitoring period. Leachate FSL's WDR's require monitoring leachate flow rate,pH, and Electrical Conductivity on a monthly basis (Table 4). Leachate volumetric data for several months indicates reasonable average flow rates. Vadose Zone Soil Gas First Semester Results Vadose zone soil gasses are generally measured at internal soil gas wells within the property boundary,not from perimeter migration monitoring wells. Soil gasses were sampled on September 3, 2010. 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-14A(Appendix I). VOCs were detected in all soil gas samples (Table 5). The highest concentration of any VOC was found in SG-1. Freon 12 was most often reported with the highest concentration in a sample. The most VOCs (thirteen)were reported SG-1. The source of the VOCs in the vadose zone is likely the old unlined portion of the landfill. Placement of a liner over a portion of this older refuse could also be a contributing factor. Methane was detected in one internal soil gas well this semester; however, measurement of methane at the perimeter migration monitoring wells indicates that the facility is compliant with Title 27 regulations for off-site migration. VOCs have been detected in soil gas since monitoring began in October 2003,but VOC impact to groundwater has only been sporadic with diminished detections since February 2002. The sporadic detection of VOCs in groundwater indicates that the presence of VOCs in the soil at these concentrations is not a significant threat to groundwater at this landfill. Soil Gas Trench Methane continues to be detected in the soil gas trench installed under the liner of Module 1. Methane content in the gas beneath the liner of Module 1 is presently between 5% and 30%. When Module 1 liner was first installed in 2003,the gas beneath the liner was found to vary between 0 and 2%. The HDPE liner was extended over Module"I"refuse in the fall of 2006. It is possible that placing a HDPE barrier over Module"I"refuse has trapped landfill gas beneath the liner. Foothill Sanitary Landfill g Department of Public Works/Solid Waste 2nd Semester and Annual 2010 Groundwater Monitoring County of San Joaquin—January 31,2011