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Leachate samples are analyzed for the following COCs every 5 years: • Total Organic Carbon • Inorganics (dissolved) • VOCs (extended list) • Semi-Volatile Organic Compounds • Chlorophenoxy Herbicides • Organophosphorous Compounds 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 The concentration of Chloride (10 mg/L) slightly exceeded the concentration limit (9.9 mg/L) in MW-3. However, if the concentration limit is rounded to one significant figure (10 mg/L) no exceedence would have occurred. In addition, the concentration is well below drinking water 1 Foothill Sanitary Landfill 6 Department of Public Works/Solid Waste 2nd Semester Groundwater Monitoring County of San Joaquin-January 31,2007