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Groundwater ® Monitoring and Field Parameters First quarter general water quality results (Table 2) indicate compliance with concentration limits where limits could be determined with the exception of Nitrate as Nitrogen detected at concentrations of 2.8 mg/L and 2.7 mg/L in wells MW-2R, and MW-3. These values slightly exceeded the concentration limit of 1.8 mg/L calculated from MW-4 data, however,these concentrations are below the US EPA and California Maximum Contaminant Level (MCL) and the California Public Health Goal (PHG) of 10 mg/L. Two VOCs (1,1-Dichloroethene and Trichloroethene)were reported in MW-3 in the January 2011 sampling event at concentrations of 0.55 ug/L and 1.2 ug/L. The well was resampled in April 2011. 1,1- Dichloroethene (1,1 DCE)was reported at 0.64 ug/L and Trichloroethene (TCE)was reported at 1.2 ug/L and these compounds were again deteted(Tables 2 and 3). These concentrations are below the MCLS for these compounds of 6 ug/L for 1,1 DCE and 5 ug/L for TCE, and the US EPA and PHG of 10 ug/L for 1,1 DCE and 1.7 ug/L for TCE. However,the County is planning to increase the corrective action(landfill gas collection)to correct this situation. In addition,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 January or April 2011 sampling events. Surface Water Surface water samples were taken upstream and downstream from the creek flowing along the eastern property boundary during the first semester 2011. The results of analyses were similar and unremarkable, showing that the surface water contribution from the landfill property to the stream did not degrade the quality of the stream (Table 4). In fact,the downstream sample had a lower concentration in both total dissolved solids and electrical conductivity than the upstream sample,possibly indicating that the surface water from the landfill contains less of these components than contributions upstream,that is,that the water entering the creek from the landfill is cleaner than the water in the creek when it enters the property. 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. Leachate Waste Discharge Requirements require monitoring leachate flow rate,pH, and Electrical Conductivity on a monthly basis (Table 6). 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 this 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 Foothill Sanitary Landfill 9 Department of Public Works/Solid Waste Vt Semester 2011 Groundwater Monitoring County of San Joaquin—July 31,2011