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i Sanitas®calculations of tolerance limits for intrawell analysis call for less than 50 background observations. In cases where the total number of observations is more than 50, and there is no increasing trend,the 50 most recent observations are used to calculate intrawell tolerance limit. Concentration limits are not updated if the data contains more than 50%non-detects or if there is a statistically significant increasing trend in the data. In these cases, the concentration limit listed in the current WDRs is compared to the most recent data. A Rank Sum analysis is performed in cases where concentration limits cannot be updated. The Rank Sum analysis determines if there is a significant difference between the median concentrations of the compliance and background data. A Mann-Kendall trend analysis of all monitoringparameters for MW-2 is conducted P quarterly in accordance with WDR Order No. 96-139. The results of a statistical analysis of trends in VOC concentrations in well MW-2 are shown on Table 1. Surface Water Concentration limits for surface water constituents are determined by the inter well tolerance limit method using Sanitas software. Analytical results from the upstream monitoring point S-1 provide the background data for this analysis. Compliance is verified if current test result from monitoring point S-2 (downstream)is within the tolerance limit. Tolerance limits are updated every time surface water is available. MONITORING RESULTS Groundwater Summary Groundwater elevations were measured and samples collected from all groundwater monitoring wells on January 10, 2007. EC was detected in well - MW 3 at a concentration of 241 uS/cm,which exceeded its tolerance limit of 130 uS/cm. However, it did not exceed the secondary maximum contaminant level of 900 uS/cm. No general water quality parameters were exceeded in wells MWA, MW-2, and MW-4 this quarter. Three VOCs were reported in MW-2 this quarter. No VOCs were reported in the other wells. No parameters were found in any of the Quality Control Blanks this quarter. MW-1 (U adient,) No general water quality parameters were exceeded in MW-1 this quarter. However, there is a statistically significant increasing trend in EC. As stated in previous reports (beginning with the fourth quarter 2004), the cause of the trend is believed to be other than the landfill because this well is up-gradient. Harney Lane Sanitary Landfill Department of Public Works/Solid Waste 1 t Quarter 2007 Groundwater Monitoring Report County of San Joaquin—Aptil 15,2007 4