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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-913, and MW-l0A) during the third quarter 2007 monitoring event. The analytical results from samples collected at these wells are used to determine potential landfill-related impacts. During the third quarter 2007 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. Third quarter 2007 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. For VOCs, only those VOCs with third quarter 2007 detections in background or detection monitoring wells were plotted. The concentration limits were developed using data collected through the third quarter 2007. 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-913 and MW-10A, chloride at MW-913 and MW-10A, magnesium at MW- 10A, field pH at MW-9A and MW-10A,potassium at MW-9A,MW-913, and MW-10A,and field temperature at MW-9A,MW-913, 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, CH2M 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. Chloride at MW-l0A was the only constituent that both exceeded its concentration limit and exhibited an increasing trend according to Sen's Slope analysis. The third quarter 2007 chloride concentration at MW-l0A (5 10 mg/L) is comparable to concentrations observed at that well intermittently since April 2002. Field specific conductance at MW-l0A and sulfate at MW-913 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, field specific conductance at MW-7A, sulfate at MW-7A, total dissolved solids at MW-7A, and field turbidity at MW-7A, MW-9A, and MW-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 was one VOC detection above the laboratory practical quantitation limit (PQL) in a detection monitoring well during the third quarter 2007 monitoring event. Trichlorofluoromethane was detected in detection monitoring well MW-9A at a concentration of 0.72 ug/L. Trichlorofluoromethane at MW-9A does not exhibit an increasing trend according to Sen's Slope analysis. 1,2-Dichloroethane was detected at MW-9B at a concentration(0.21 ug/L)below the laboratory PQL. 2