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steady-state gas composition indicated that the well was purged. After purging, gas samples <br /> were collected in 6-liter Summa canisters and sent to Atmospheric Analysis and Consulting, Inc. <br /> for analysis by EPA method TO-14A. <br /> Leachate <br /> Leachate at each sump is monitored monthly for the following field parameters: <br /> Electrical conductivity pH <br /> Samples collected from the leachate sumps are analyzed for the following semiannual <br /> monitoring parameters: <br /> TDS Calcium <br /> Chloride Magnesium <br /> Carbonate Potassium <br /> Bicarbonate Sodium <br /> Nitrate-Nitrogen VOCs (Short List) <br /> Sulfate <br /> Statistical Analysis of Groundwater Data <br /> The NCRCSL has been approved to perform interwell tolerance limits (up-gradient well serves <br /> as the background). Concentration limits are updated once yearly using interwell tolerance limit <br /> methods, and were most recently updated for the second semester of 2005. Analytical results <br /> from this monitoring event were compared to the concentration limits. <br /> Concentration limits are updated where possible. If the historical data contains more than 50% <br /> non-detects, the concentration limit cannot be updated. In these cases, the established <br /> concentration limit listed in the WDRs is used for comparison. <br /> A Rank Sum analysis is also performed if concentration limits cannot be updated. The Rank <br /> Sum analysis determines if there is a significant difference between the median values of <br /> historical and recent concentrations within a well. Concentration limits are updated on a yearly <br /> basis in accordance with the latest WDRs. As requested by RWQCB staff, stiff diagrams will be <br /> included in the second semester and annual report. <br /> North County RCSL 6 Public Works/Solid Waste <br /> 1 st Semester 2006 Groundwater Monitoring County of San Joaquin—July 31,2006 <br />