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Vadose Zone Soil Gas Second 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 September 11, 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 all 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-10. The source of the VOCs in the vadose zone is likely the old unlined portion of the landfill. Methane was detected in three 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 third and fourth quarters. Groundwater was determined to flow towards the east-southeast(Figures 3 and 4). The calculated average linear groundwater flow velocity in the third quarter was 79.21 feet per year based on a hydraulic gradient of 0.00235 foot per foot. The calculated average linear groundwater flow velocity in the fourth quarter was 76.95 feet per year based on a hydraulic gradient of 0.002285 foot per foot (Appendix F). STANDARD OBSERVATIONS Regular site inspections were performed during the second semester of 2013. Monthly standard observations have been summarized(included in CD that accompanies report). The electronic signatures on the forms certify that all observations were performed and are accurate. RUN-OFF/RUN-ON FACILITIES The Foothill Sanitary Landfill utilizes several methods to control run-on and run-off. The natural topography of the area controls any run-on into the site. Also,the working area is a significant distance from the property boundary and at a higher elevation, so run-on from surrounding properties into refuse is not possible. To control run-off, a perimeter ditch along the north, west and east ends of the unit directs all storm water run-off into a sedimentation basin on the east side of the site. The rest of the run-off from the unit gathers into a sedimentation basin at the southeast corner of Area 1. There were no breeches to any of the run- on/run-off facilities during this monitoring period. Foothill Sanitary Landfill 9 Department of Public Works/Solid Waste 2nd Semester and Annual 2013 Groundwater Monitoring County of San Joaquin—January 31,2014