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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,with an upgradient well providing background data(Tables 2 &3). MW-4 was located directly up-gradient of the landfill based on groundwater elevations from the previously-installed wells. This well has been sampled nine times since installation. Concentration limits have been established based on Sanitas software calculations using data for MW-4. Groundwater Monitoring and Field Parameters A review of the first and second quarter general water quality parameters (Tables 2 & 3) indicates compliance with concentration limits where limits could be determined with the exception of the parameters discussed below: • Carbonate Alkalinity detected at a concentration of 3.1 mg/L during the 1 St quarter sampling event in well MW-3 slightly exceeded the concentration limit of 2.5 mg/L calculated from MW-4 data. Carbonate Alkalinity is generally non-detect in the site wells and leachate. The species of Alkalinity generally present in groundwater at the site, Bicarbonate Alkalinity was less than the concentration limit in all wells. Since there is no maximum contaminant level for this parameter and the detected concentration was low, this detection is not considered an impact on water quality. • Nitrate as Nitrogen detected at a concentration of 3.1 mg/L at cross-gradient well MW-1, and at lower concentrations in wells MW-2R, and MW-3. These values slightly exceeded concentration limit of 1.8 mg/L calculated from MW-4 data. Because the concentration was higher in cross-gradient well MW-1 than in down-gradient wells,the reported levels of Nitrate in wells MW-2R and MW-3 are likely representation of natural background conditions and not a result of a release from the landfill. In addition, the Nitrate was non- detect in leachate. VOCs One VOC (toluene)was reported in MW-1 in the February 2010 sampling event at 18 ug/L in MW-1. The well was resampled in May 2010, and Toluene was reported in a trace concentration of 0.48 ug/L. VOCs were not detected in any other well during the February or May 2010 sampling events. Toluene was last detected in MW-1 in the 1St quarter 2001. These are sporadic low concentration VOC detections that are generally not persistent at the well. Foothill Sanitary Landfill 8 Department of Public Works/Solid Waste 15`Semester 2010 Groundwater Monitoring County of San Joaquin—July 21,2010