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Samples for VOC analysis are collected from each well. Where combustible gas is detected, the VOC sample will be collected from the probe with the highest methane content. Where no combustible gas is detected, the VOC sample will be collected from the deepest probe unless the sampling technician determines that there may be an obstruction to the probe, in which case a sample is collected from the next higher probe. Statistical Analysis of Groundwater Samples At the CHSL, the County has been approved to use the intrawell tolerance limit method(each well provides its own background data) for groundwater analysis, and to use the interwell tolerance limit method for surface water analysis. Concentration limits are updated quarterly, and were most recently updated this quarter. When a statistically significant trend exists for the current data or greater than 50 percent of the data consists of non-detects or there are insufficient data, the latest calculated concentration limit is presented(Table 1). Analytical results from the current quarter monitoring event were compared to the concentration limits shown. The Sanitas®program is used for statistical analysis. Calculation of tolerance limits for intrawell analysis requires 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 current observations are used for intrawell tolerance limit analysis. If the data contains more than 50%non-detects or if there is a statistically significant increasing trend in the data, then a Rank Sum analysis is performed. The Rank Sum analysis determines if there is a significant difference between the median concentrations of the compliance and background data. Corral Hollow Landfill 6 Department of Public Works/Solid Waste 2nd Quarter 2007 Groundwater Monitoring County of San Joaquin—July 31,2007