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• Well MW-3: No General water quality parameters were exceeded during either the 1St or 2nd semester 2012 sampling events. • Well MW-4: No General water quality parameters were exceeded during the 1St semester 2012 sampling event. Turbidity was recorded at 67.9 NTU which slightly exceeded the tolerance limit of 65 NTU during the 2nd Semester 2012 sampling event. However,turbidity is an indicator of well function and not an indicator of landfill impact to groundwater. • Well MW-5: No General water quality parameters were exceeded during either the 1St or 2nd semester 2012 sampling events. VOCs Two VOCs (Trichloroethene, and 1,1-Dichloroethene)were reported in samples collected from well MW-3 during the 1St semester 2012 . VOCs were not detected in any wells in the 2nd Semester 2012 . These detections will continue to be scrutinized in the future. As previously described,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. VOCs were not detected in any other well during 2012. The County continues to be concerned that installation of impermeable liner over refuse decreases the potential venting of LFG in spite of the presence of a LFG collection system. Sealing the refuse from the air can increase the potential for contamination of groundwater by LFG entering the soil beneath the landfill. Storm Water Storm water was not sampled during the 1St Semester 2012. Storm water was sampled from discharge points SW-UP and SW-DWN in Second Semester 2012 (Appendix Q. Results were unremarkable. Surface Water Surface water samples were collected in the 2nd Semester 2012 . . The results of previous analyses of the upstream and downstream samples were similar, showing that the surface water contribution to the stream did not degrade the quality of the stream. Note that the creek receives contribution from the ground surface and several smaller creeks from the neighboring 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, carrying residue from the cattle, and is included in the samples taken. HISTORICAL TIME SERIES PLOTS AND STIFF DIAGRAMS Constituents not detected are plotted at a value of half their respective detection limits in the Historical Time Series Plots (Appendix F). Outliers were included in the plots as directed by RWQCB staff. Stiff diagrams are submitted annually with the second semester and annual report. The stiff diagrams submitted for the first and second semesters indicate a calcium-bicarbonate water type since these ions have the highest concentrations in the six wells (Appendix F). The water type is similar in all wells as indicated by similarity in concentrations of the various constituents and the similarity in diagram shapes. This similarity indicates that the groundwater is not impacted as it moves under the landfill. The shapes of the diagrams between the first and second semesters are also very similar, indicating that the general Foothill Sanitary Landfill 12 Department of Public Works/Solid Waste 2nd Semester and Annual 2012 Groundwater Monitoring County of San Joaquin—January 15,2013