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been reported in any other well. Fensulfothion was reported in the first quarter data, but not found in the second quarter. MW-5 is a significant distance from the landfill (Figure 3), therefore the detection of one Organophosphate Pesticides at is not likely related to the landfill. The County will continue to analyze all wells for organophosphates. Surface Water Surface water samples were not available this semester. Leachate Waste Discharge Requirements require monitoring leachate flow rate, pH, and Electrical Conductivity on a monthly basis (Table 4). Leachate volumetric data for several months indicates unreasonable average flow rates, possibly due to a slowly failing meter battery. Battery failure was not apparent at that time. The battery was replaced in mid-May. Vadose Zone Soil Gas Soil gasses were sampled on January 29, 2008. 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 5). The highest concentration of any VOC was found in SG-T#1. Freon 12 was most often reported with the highest concentration in a sample. The most VOCs (eleven) were reported in SG-10 and SG-11. Methane concentrations were 0 percent in all the wells except for 0.2 percent in SG-1. 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 direction and flow rate is based on groundwater elevations at 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 134.66 feet per year based on a hydraulic gradient of 0.004 foot per foot. The calculated average linear groundwater flow velocity in the second quarter was 127.9 feet per year based on a hydraulic gradient of 0.0038 foot per foot (Appendix G). The top of casing elevations for MW-4 and 5 is scheduled for August 2008. Foothill Sanitary Landfill 9 Department of Public Works/Solid Waste 1"Semester 2008 Groundwater Monitoring County of San Joaquin—July 31,2008