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2.0 Groundwater Monitoring Program Groundwater samples were collected by ATC Associates Inc. from two background monitoring wells (MW-6A and MW-7A) and four detection monitoring wells (MW-8A, MW-9A, MW-9B, and MW-10A) during the first quarter 2008 monitoring event. The analytical results from samples collected at these wells are used to determine potential landfill-related impacts. During the first quarter 2008 monitoring event, analysis for field parameters (pH, specific conductance, temperature, and turbidity) and monitoring parameters (bicarbonate, calcium, carbonate, chloride,magnesium,nitrate,potassium, sodium, sulfate, total dissolved solids [TDS], and volatile organic compounds [VOCs]) was performed for the background monitoring wells and detection monitoring wells. First quarter 2008 field and laboratory sampling results from background and detection monitoring wells are summarized on Table 2.2, along with the concentration limits determined from background monitoring well data. The historical groundwater data for the background and detection monitoring wells are presented in Appendix D. The data are graphed on time series concentration plots in Appendix E. The concentration limits were developed using data collected through the first quarter 2008. The statistical analysis calculations are presented in Appendix E. A copy of the statistical analysis methodology is presented in Appendix C. As presented on Table 2.2, the following constituents exceeded their respective concentration limits: calcium at MW-9B, chloride at MW-9 , potassium at MW-9B, and field temperature at MW-9A, MW-9B, and MW-10A. The chloride concentrations (with high specific conductance values) could indicate a saltwater intrusion to the groundwater. The French Camp Landfill is within the central Stockton area impacted by saltwater intrusion (Fourth Quarter/Annual 1999 Monitoring Report, French Camp Landfill, C2M HILL, January 2000). Historical data from the background and detection monitoring wells were evaluated for temporal trend using Sen's Slope trend analysis. Graphs of the Sen's Slope analyses are included in Appendix E. Bicarbonate at MW-7A, chloride at MW-10A, field specific conductance at MW-6A, and sulfate at MW-9B exhibited increasing trends, but did not exceed their respective concentration limits. Sen's Slope analysis identified decreasing trends in the following constituents: nitrate at MW-8A and MW-10A, field pH at MW-6A, sulfate atMW-7A, total dissolved solids at MW-7A, and field turbidity at MW-7A, MW-9A, and -10A. As noted above, MW-6A and MW-7A are background monitoring wells, and trends in the groundwater quality at these wells are not indicative of an impact from the facility. As presented in Table 2.2,there were no VOCs detected in detection monitoring wells during the first quarter 2008 monitoring event. 2