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Leachate samples were last analyzed for COCs during the first semester 2005 monitoring event. The next monitoring event for leachate COCs will occur during the first semester of 2010. Vadose Zone Soil Gas The soil is monitored for VOCs per the WDRs Order No. R5-2003-0020. Eleven wells, SG-1 through SG-11, are located around modules "I" and 1 (Figure 5). Well depths range from 25 feet to 68 feet. Gas from the soil gas trench under Module 1, designated SG-T, is also analyzed for VOCs. The Monitoring and Reporting Program requires that soil gas be monitored semi-annually. Samples are analyzed by a certified laboratory per EPA test method TO-14A. MONITORING RESULTS Sampling and analysis procedures are in Appendix A and the field data sheets are in Appendix B. The laboratory reports are in Appendix C. Statistical Analysis The FSL has been approved to use interwell tolerance limits methods (up-gradient well provides the background data). Analytical results from this monitoring period were compared to the concentration limits (Table 2). Tolerance limits for five of the general water quality parameters were determined using statistical analysis. The other limits shown were taken from the WDRs. The statistical analysis is described in Appendix D. Groundwater Monitoring and Field Parameters No general water quality parameters were exceeding in any of the wells this semester with the exception of Turbidity in well MW-4 (48.1 mg/L). However,because the tolerance limit for turbidity is 48 mg/L, this exceedence is considered insignificant. This is the first time this well was sampled, and the turbidity could be an artifact of the well installation. VOCs Acetone was reported in samples collected on July 23, 2007 from wells MW-1,MW-2R, and MW-3. Because this compound was found simultaneously in both up-gradient and down-gradient wells, and because this compound is a common laboratory contaminant(as identified in WDR section E-18),we speculate that we are again seeing laboratory contamination. In addition, Trichloroethene (TCE) was reported in the sample collected from well MW-3. No VOC analytes were detected in any of the laboratory control blanks this semester. COCs COC samples for the new wells MW-4 and MW-5 were collected on July 23, 2007. Trace concentrations of semi-volatile compound Di-n-butyl Phthalate (identified as a common laboratory contaminant in WDR section E-18)were reported in both wells and in laboratory control blanks. No other semi-volatile Foothill Sanitary Landfill 8 Department of Public Works/Solid Waste 2`d Semester and Annual 2007 Groundwater Monitoring County of San Joaquin—January 31,2008