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MONITORING RESULTS Groundwater Summary Groundwater was sampled on January 23, 2012. No general water quality parameters were 1 exceeded this quarter with the exception of Bicarbonate Alkalinity in SB-1, MW-4, and MW-5. The Alkalinity was measured above the concentration limit in these wells, but is no primary or secondary maximum contaminant level (MCLs) for alkalinity; therefore,these exceedances are of concern, but do not pose a human health risk. The primary MCL for Nitrate as Nitrogen was exceeded in wells MW-4, MW-5 and MW-8 this quarter. The secondary MCL for EC was exceeded in all wells this quarter. The secondary MCL was also exceeded for TDS in wells SB-1, MW-4, MW-5, MW-6, and MW-7. In addition, the secondary MCL was exceeded for Sulfate in wells MW-4, MW-6, and MW-7. Ten VOCs were detected in impacted well MW-5 and seven VOCs were detected in well MW-8. All of the VOCs detected in MW-8 were also detected in MW-5. One VOC (Tetrachloroethene) was detected above its MCL in MW-5 and MW-8 this quarter. The source of these VOCs is apparently from LFG emanating from the refuse discovered near the property boundary line, where the influence of the LFG system has been minimal. As a corrective action measure,the County installed five additional LFG wells installed in this area in December 2008 and has since increased the collection rate from those wells. No VOCs were reported in the deep aquifer wells. No VOCs were reported in shallow aquifer wells SB-1 and MW-4 this quarter. Chloroform was detected in the field blank this quarter. The source of the VOCs in the field blank is likely from laboratory contamination. Shallow Aquifer SB-1(Up gradient): Concentrations of all the parameters analyzed were within established concentration limits this quarter except for Bicarbonate Alkalinity (Table 1). However,because there are no primary and secondary MCLs for Bicarbonate Alkalinity,this exceedance does not pose a human health risk. No primary MCLs were exceeded this quarter in SB-l. Secondary MCLs for EC and TDS were exceeded in SB-1 this quarter. However, the EC and TDS levels are consistent with the general historical conditions at this well. A"significantly decreasing"trend is reported by the Sanitas program for Turbidity, chloride and sulfate this quarter, and a"significant increasing"trend is reported for pH, EC, and TDS this quarter(Table 3). However,the variation in concentrations are slight, so the reports of "significant trend"appears to be an artifact of the Sanitas statistical calculations. Corral Hollow Sanitary Landfill 9 Department of Public Works/Solid Waste 1 Quarter 2012 Groundwater Monitoring County of San Joaquin—April 16,2012