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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 first 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 well MW-3 where Bicarbonate Alkalinity was slightly exceeded. The elevated level of Bicarbonate Alkalinity at MW-3 is unusual,however,this level of detection has been present in the past. Groundwater elevations for the 2nd quarter 2013 are similar to previous results (Table 3). One VOC was reported in concentrations not exceeding 1 ppb at MW-3 in the samples collected in February 2013 (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 that 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 g sampling.other well during this . VOCs have not been detected at any other p g groundwater monitoring well. In addition,the Bicarbonate Alkalinity exceedence at MW-3 is also likely due to the LFG intrusion through the vadose zone from the gas-tight HDPE membrane over Area"I". Surface Water Surface water samples were last taken December 15, 2012. Surface water samples were last taken upstream and downstream from the creek flowing along the eastern property boundary. Results were 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. Storm Water Storm water was sampled from discharge points SW-UP and SW-DWN in December 2012 (Appendix C). Results were unremarkable. Foothill Sanitary Landfill 8 Department of Public WorkslSolid Waste 1 sc Semester 2013 Groundwater Monitoring County of San Joaquin—July 25,2013