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