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® MONITORING RESULTS Groundwater Monitoring and Field Parameters The concentration of Sulfate is below the concentration limit at background well MW-1 for the second straight semester. The Sulfate concentration had exceeded the limit the first semester 2004. This is an indication that regional changes in general water quality conditions may be reflected in groundwater samples taken at the landfill. Since the concentration limits of many of the general water quality parameters are relatively low, slight regional changes in the water quality could cause the concentration exceedences observed in MW-3. The concentration limit of Nitrate-Nitrogen in MW-3 was slightly exceeded the previous semester, but is now below the concentration limit. The concentration limit of Magnesium in MW-3 was slightly exceeded the previous semester,but is now below the concentration limit. The concentration of Chloride in MW-3 slightly exceeded the concentration limit (Table 2). The exceedence of Chloride occurred the previous semester. The concentration of Chloride is well below the secondary maximum contaminant level (California DHS) and is modestly higher than the concentration of Chloride in MW-1,which is up-gradient. The concentration of Sodium in MW-3 slightly exceeded the concentration limit (Table 2). The concentration limit of Sodium was established for the first time this quarter because there was sufficient data. There is no drinking water standard for Sodium. The concentration of Sodium is modestly higher than the concentration of Sodium in MW-1, which is up-gradient. VOCs No VOCs were reported this semester with the exception of"false positives" in MW-2R and MW-3. The last VOC reported, with the exception of"false positives," occurred in samples retrieved on October 14, 2002. COCs COCl were sampled/tested on July 22, 2004. Other than a trace concentration of Bis(2-ethylhexyl)phthalate in well MW-3,no semi-volatiles were reported. Well MW-3 was retested this semester for Bis(2-ethylhexyl)phthalate, and again the compound was reported. Note that Bis (2-ethylhexyl)phthalate is a common laboratory contaminant and the presence of this compound will be monitored with future sampling and analysis. Foothill Sanitary Landfill 7 Department of Public Works/Solid Waste 1sT Semester 2005 Groundwater Monitoring County of San Joaquin-July 29,2005