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Statistical Analysis The FSL has been approved to use interwell tolerance limits methods,with an upgradient well providing ® background data(Tables 2 & 3). MW-4 was located directly up-gradient of the landfill based on groundwater elevations from the previously- installed wells. This well has been sampled thirteen times since installation. Concentration limits have been established based on Sanitas software calculations using data for MW-4. Groundwater Monitoring and Field Parameters Monitoring results for the second semester sampling event(Table 2) indicate that the concentrations of field and monitoring parameters are below established concentration limits where limits could be established for all wells,with the exception of wells MW-1 where EC was slightly exceeded and MW-4 where a slight exceedence for Turbidity were reported. The elevated level of EC at MW-1 is unusual,however,this level of detection has been present in the past. In addition, MW-1 is not downgradient from the landfill and this level of detection of EC at this time in this well is not an indication of landfill impact to groundwater. Also, turbidity is an indicator of well function and not an indicator of landfill impact to groundwater. Groundwater elevations for the 40"quarter 2012 are similar to previous results (Table 3). VOCs were not detected in any wells during this sampling event(Table 2). VOCs have periodically been detected in MW-3 since the 1St Quarter 1995 sampling event. In response to recent detections of VOCs in well MW-3 that started during the 1St Semester 2011 sampling event,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 Area"I"refuse (see Compliance History, above). Placing a plastic cover over unlined refuse can reduce natural venting of LFG 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. Based on the results of the 2nd Semester 2012 monitoring event,there are no landfill related impacts to groundwater. Surface Water Surface water samples were taken December 15, 2012. Surface water samples were last taken upstream and downstream from the creek flowing along the eastern property boundary. Results are unremarkable. The composition of the downstream sample was equivalent to the upstream sample. For most constituents, including nitrate nitrogen and TDS, downstream concentrations were equal to or less than upstream concentrations, indicating that drainage from the property into the creek did not impact water quality(Appendix C). Note that, when flowing, surface water from adjacent properties on which cattle is grazed properties. Run- off from those properties enters the stream, and is included in the samples taken. Such run-off can carry the result of cattle defecation and residue of any agricultural chemicals applied. Foothill Sanitary Landfill 8 Department of Public Works/Solid Waste 2nd Semester and Annual 2012 Groundwater Monitoring County of San Joaquin—January 15,2013