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Statistical Analysis Groundwater At the Harney Lane Landfill, the intrawell tolerance limit method(each well provides its own background data)has been approved for groundwater analysis, whereas the interwell tolerance limit method has been approved for surface water analysis. Concentration limits are updated quarterly, where possible, and were most recently updated in this quarter. Analytical results were compared to the concentration limits shown in Table 1. ' 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 monitoring parameters for MW-2 is conducted 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 April 2, 2007. No general water quality parameters were exceeded in wells MW-1, MW-2, MW-3 and MW-4 this quarter. Harney Lane Sanitary Landfill Department of Public Works/Solid Waste 2nd Quarter 2007 Groundwater Monitoring Report County of San Joaquin—July 15,2007 4