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Groundwater Monitoring and Field Parameters Concentrations of all parameters were within established concentration limits where the limits could be determined during the first quarter 2012 sampling event(Table 2). Two VOCs are reported in concentrations not exceeding 1 ppb at MW-3 in the samples collected in January 2012 (Table 2). These results are consistent with the samples collected last year. In response the County has increased the corrective action(landfill gas collection) to correct this situation. Improvements installed in the second semester 2011 include the replacement LFG well GX-2A and increase in LFG pipe size to better serve GX-7 and-9. Efforts to further increase LFG collection continue. The County suspects that this new detection of VOCs at MW-3 is related to the placement of a gas-tight HDPE membrane over Module"I"refuse (see Compliance History, above). Placing a plastic cover over unlined refuse can reduce natural venting of landfill gas and increase transport of VOC-containing LFG through the vadose zone towards the water table. Detection at this time, approximately five years after installing the liner over refuse, is consistent with the lag time experienced for other actions at this landfill. VOCs were not detected in any other well during this sampling. VOCs have not been detected at any other groundwater monitoring well. Surface Water Surface water samples were not taken this semester due to lack of rain. Surface water samples were last taken upstream and downstream from the creek flowing along the eastern property boundary during the first semester 2011. These results were discussed in the First Semester 2011 Report. Note that,when flowing,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(and defecation). Surface water from these adjacent properties also enters the stream, and is included in the samples taken. Storm Water There were no stormwater discharges from the site during this monitoring period. Leachate Waste Discharge Requirements require monitoring leachate flow rate,pH, and Electrical Conductivity on a monthly basis (Table 5). Leachate volumetric data for several months indicates reasonable average flow rates. Leachate is returned to the refuse in accordance with the WDRs for this landfill. The landfill operator has constructed two infusion points(a"dry well") in the refuse to receive this leachate. Vadose Zone Soil Gas First 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 April 12, 2012. Samples were collected by first measuring the methane content using a CES- Foothill Sanitary Landfill 11 Department of Public Works/Solid Waste 1s`Semester 2012 Groundwater Monitoring County of San Joaquin—July 17,2012