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2.0 Groundwater Monitoring Program is Groundwater samples were collected by ATC Associates Inc. from two background monitoring wells (MW -6A and MW -7A), four detection monitoring wells (MW -8A, MW -9A, MW -9B, and MW- l0A), and one evaluation monitoring well (MW -2) during the first quarter 2007 monitoring event. ATC Associates Inc. reported that evaluation monitoring well MW- lA was obstructed and could not be sampled during the first quarter 2007. The analytical results from samples collected at these wells are used to determine potential landfill -related impacts. The well screens forMW-IA and MW -2 are located in waste material. The analytical results from MW-lA and MW -2 are used to evaluate the changes in water quality within the landfill. During the first quarter 2007 monitoring event, analysis for field parameters (pH, specific conductance, temperature, and turbidity) and monitoring parameters (barium, bicarbonate, calcium, carbonate, chloride, magnesium, nitrate, potassium, sodium, sulfate, and total dissolved solids [TDS]) was performed for the background monitoring wells, detection monitoring wells, and evaluation monitoring wells. 2.1 Results for Detection Monitoring Wells First 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 is concentration plots in Appendix E. For VOCs, only those VOCs with first quarter 2007 detections in background or detection monitoring wells were plotted. The concentration limits were developed using data collected through the first 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: barium at MW -9B, calcium at MW -10A, chloride at MW -10A, magnesium at MW -10A, pH at MW -10A, potassium at MW -913 and M -10A, and 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, CH2MHILL, 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 W-l0A was the only constituent that both exceeded its concentration limit and exhibited an increasing trend according to Sen's Slope analysis. The first quarter 2007 chloride concentration at MW-l0A (520 mg/L) is comparable to concentrations observed at that well intermittently since April 2002. The following constituents exhibited an increasing trend, but did not exceed their respective concentration limits: barium at MW -9A and sulfate at MW -913. Sen's Slope analysis identified decreasing trends in the following constituents: barium at MW -913, pH at MW -6A, nitrate at MW -8A and MW -10A, specific conductance at -7A, sulfate at MW -7A, and turbidity at MW -7A, MW -9A, and MW -10A. As noted above, MW -6A and MW -7A are background N