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Surface Water Surface water samples were taken from the creek flowing along the eastern property boundary during the first semester 2010. The results of analyses of the upstream and downstream samples were similar, showing that the surface water contribution to the stream did not degrade the quality of the stream(Table 4). In fact,the downstream sample had a lower concentration in both total dissolved solids and electrical conductivity than the upstream sample,possibly indicating that the surface water from the landfill contributes less to the stream than upstream surface water. Note that the creek receives contribution from the ground surface and several smaller creeks on the neighbor's properties east of the creek, and that these surfaces and the creek itself are subject to cattle grazing. Surface water from these properties also enter the stream, and is included in the samples taken. Leachate Waste Discharge Requirements require monitoring leachate flow rate,pH, and Electrical Conductivity on a monthly basis (Table 6). 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 soil gas wells within the property boundary,not from perimeter migration monitoring wells. Soil gasses were sampled on February 2, 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 7). The highest concentration of any VOC was found in SG-l. Freon 12 was most often reported with the highest concentration in a sample. The most VOCs (fourteen) were reported in the soil gas trench(sample SG-T1). The source of the VOCs in the vadose zone is likely the old unlined portion of the landfill. Methane was detected in three soil gas wells 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 condition at this landfill. Foothill Sanitary Landfill g Department of Public Works/Solid Waste 1S`Semester 2010 Groundwater Monitoring County of San Joaquin—July 21,2010