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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 third quarter 2011 sampling event(Table 2). Two VOCs(1,1-Dichloroethene and Trichloroethene) are reported in concentrations below 2 ppb at MW-3 in the samples collected in August 2011. 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. 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 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 the 2nd semester 2011 sampling event that was conducted on August 9, 2011. 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 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 4). 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. Although an unusually large amount of rain fell on the site last winter, County staff does not believe that this, in itself, explains the high collection rate in March. One explanation of the observations is that the infusion points became saturated, and a portion of the leachate channeled from the infusion point through the refuse to the leachate collection and recovery system, where it was collected in the sump again. As a result of this observation,the landfill operator temporarily diverted leachate directly to the active face, where the leachate is absorbed by dry, incoming refuse, and constructed a supplementary diffusion point in another area of the refuse.. Foothill Sanitary Landfill 8 Department of Public Works/Solid Waste 2°d Semester and Annual 2011 Groundwater Monitoring County of San Joaquin—January 31,2012