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During the fourth quarter 2007 monitoring event, analysis for field parameters (pH, specific
<br /> conductance, temperature, and turbidity) and monitoring parameters (bicarbonate, calcium,
<br /> carbonate, chloride, magnesium,nitrate, potassium, sodium, sulfate, total dissolved solids [TDS],
<br /> and volatile organic compounds [VOCs]) was performed for the background monitoring wells
<br /> and detection monitoring wells.
<br /> Fourth quarter 2007 field and laboratory sampling results from background and detection
<br /> monitoring wells are summarized on Table 2.2, along with the concentration limits determined
<br /> from background monitoring well data. The historical groundwater data for the background and
<br /> detection monitoring wells are presented in Appendix D. The data are graphed on time series
<br /> concentration plots in Appendix E. For VOCs, only those VOCs with fourth quarter 2007
<br /> detections in background or detection monitoring wells were plotted. The concentration limits
<br /> were developed using data collected through the fourth quarter 2007. The statistical analysis
<br /> calculations are presented in Appendix E. A copy of the statistical analysis methodology is
<br /> presented in Appendix C.
<br /> As presented on Table 2.2, the following constituents exceeded their respective concentration
<br /> limits: calcium at MW-9B and MW-10A, chloride at MW-9B and MW-10A, magnesium at MW-
<br /> 9B and MW-10A, field pH at MW-9A and W-10A, potassium at MW-8A, MW-9A, MW-9B,
<br /> and MW-10A, field temperature at MW-9A, MW-9B, and MW-10A, and total dissolved solids at
<br /> MW-10A. The chloride concentrations (with high specific conductance values) could indicate a
<br /> saltwater intrusion to the groundwater. The French Camp Landfill is within the central Stockton
<br /> area impacted by saltwater intrusion (Fourth Quarter/Annual 1999 Monitoring Report, French
<br /> Camp Landfill, CH2M HILL,January 2000).
<br /> Historical data from the background and detection monitoring wells were evaluated for temporal
<br /> trend using Sen's Slope trend analysis. Graphs of the Sen's Slope analyses are included in
<br /> Appendix E. Chloride at MW-l0A and potassium at MW-l0A were the only constituents that
<br /> both exceeded their respective concentration limits and exhibited increasing trends according to
<br /> Sen's Slope analysis. The fourth quarter 2007 chloride concentration at MW-l0A (470 mg/L) is
<br /> comparable to concentrations observed at that well intermittently since May 2001. The fourth
<br /> quarter 2007 potassium concentration at W-l0A (3.3 mg/L) is higher than concentrations
<br /> previously observed at that well, but is consistent with potassium concentrations observed at
<br /> downgradient well MW-9B,which does not exhibit an increasing trend.
<br /> Bicarbonate at MW-7A, field specific conductance at MW-10A, and sulfate at MW-9B exhibited
<br /> increasing trends, but did not exceed their respective concentration limits. Sen's Slope analysis
<br /> identified decreasing trends in the following constituents: nitrate at MW-8A and MW-10A, field
<br /> pH at MW-6A, field specific conductance at -7A, sulfate at MW-7A, total dissolved solids at
<br /> MW-7A, and field turbidity at MW-7A, MW-9A, and MW-10A. As noted above, MW-6A and
<br /> MW-7A are background monitoring wells, and trends in the groundwater quality at these wells
<br /> are not indicative of an impact from the facility.
<br /> As presented in Table 2.2, there were no VOCs detected above the laboratory practical
<br /> quantitation limit(PQL) in detection monitoring wells during the fourth quarter 2007 monitoring
<br /> event. 1,2-Dichloroethane was detected at MW-9B at a concentration (0.26 ug/L) below the
<br /> laboratory PQL. Trichlorofluoromethane was detected at MW-9A at a concentration(0.34 ug/L)
<br /> below the laboratory PQL. Neither 1,2-dichloroetheane at MW-9B nor trichlorofluoromethane at
<br /> MW-9A exhibits an increasing trend according to Sen's Slope analysis.
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