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Soil Gas - Unsaturated Zone <br /> Soil gasses were sampled in February 2005. Samples were collected by first measuring the <br /> methane content using a Landtec GEM1000 portable gas detector. The GEM was operated until'a <br /> steady-state gas composition indicated that the well was purged. After purging, gas samples were <br /> collected in 6-liter Summa canisters and sent to Atmospheric Analysis and Consulting <br /> Laboratories for analysis by EPA method TO-14A. If the GEM indicated methane content less <br /> than 0.1%,the methane concentration was measured using a Gastech Landfill Monitor. <br /> First Semester Results <br /> VOCs were detected in all soil gas samples. Of the wells, the highest concentration of any VOC <br /> was found in SG-1 (Table 5). Toluene was most often reported with the highest concentration in a <br /> well (Appendix H). Of samples collected at the wells, the most VOCs (seventeen)were reported <br /> were in SG-1. The results are consistent with the historical record. <br /> Note that the sampling point at well SG-1 is located approximately four feet from the top of the <br /> groundwater table near groundwater well MW-3, and that no VOCs are found at MW-3. <br /> Methane concentrations were 0 percent in all the wells except for 0.1 percent in SG-1 and 1.5 <br /> percent in SG-12. <br /> The County plans to install a landfill gas extraction system by November 2006 in accordance with <br /> the Cleanup and Abatement Order. Decrease in combustible gas and VOC concentrations in the <br /> soil gas is expected after the system is put in operation. <br /> GROUNDWATER FLOW DIRECTION <br /> Groundwater elevations were measured in monitoring wells MW-1,MW-2R, and MW-3 during <br /> the first and second quarters. Groundwater was determined to flow towards the southwest <br /> (Figures 3 and 4). The groundwater gradient is 0.0022 foot per foot, calculated from the drop in <br /> water elevation from 49.5 feet to 43.0 feet MSL over a distance of 2,960 feet. <br /> STANDARD OBSERVATIONS <br /> Regular site inspections were performed during the second semester of 2004. Monthly standard <br /> observations have been compiled(Appendix G). Signatures on the forms certify that all <br /> observations were performed and are accurate. <br /> Foothill Sanitary Landfill g Department of Public Works/Solid Waste <br /> 1 sr Semester 2005 Groundwater Monitoring County of San Joaquin-July 29,2005 <br />