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collection and recovery system,where it was collected in the sump again. As a result of this observation, the landfill operator has diverted leachate directly to the active face,where the leachate is absorbed by dry, ® incoming refuse. In addition, a supplementary diffusion point will be installed. Vadose Zone Soil Gas First Semester Results Vadose zone soil gasses are generally measured at soil gas wells within the property,not from perimeter migration monitoring wells. Soil gasses were sampled on January 25, 2011. 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 1). 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 (eight) were reported SG-4. The source of the VOCs in the vadose zone is likely the old unlined portion of the landfill. Methane was detected in one interior soil gas well this semester; however, 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, with the exception of MW-3,VOC is not indicated. The presence of VOCs in the soil at these concentrations is not, in itself,a significant condition at this landfill. GROUNDWATER DIRECTION AND FLOW RATE Groundwater elevations were measured in monitoring wells during the first and second quarters. Groundwater was determined to flow towards the east-southeast(Figures 3 and 4). The calculated average linear groundwater flow velocity in the first quarter was 84.16 feet per year based on a hydraulic gradient of 0.0025 foot per foot. The calculated average linear groundwater flow velocity in the second quarter was 70.87 feet per year based on a hydraulic gradient of 0.0021 foot per foot(Appendix G). STANDARD OBSERVATIONS Regular site inspections were performed during the first semester of 2011. Monthly standard observations have been summarized(Appendix H). 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, so run-on from surrounding properties is minimal. 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 Module 1. There were no breeches to any of the run- on/run-off facilities during this monitoring period. Foothill Sanitary Landfill 10 Department of Public Works/Solid Waste 1s`Semester 2011 Groundwater Monitoring County of San Joaquin—July 31,2011