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2,0 Groundwater Monitoring Program
<br /> Groundwater samples were collected by ATC Associates Inc. from two background monitoring
<br /> wells (MW-6A and MW-7A) and four detection monitoring wells (MW-8A, MW-9A, MW-9B,
<br /> and MW-l0A) during the third quarter 2009 monitoring event. The analytical results from
<br /> samples collected at these wells are used to determine potential landfill-related impacts.
<br /> During the third quarter 2009 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 /> Third quarter 2009 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. The concentration limits were developed using data collected
<br /> through the third quarter 2009. The statistical analysis calculations are presented in Appendix E.
<br /> A copy of the statistical analysis methodology is presented in Appendix C.
<br /> As presented on Table 2.2, the following constituents exceeded their respective concentration
<br /> limits: calcium at MW-9A, MW-9B, and MW-10A, chloride at MW-9B and MW-10A,
<br /> magnesium at MW-9A and MW-10A, nitrate at MW-9A, field pH at MW-9A and MW-10A,
<br /> potassium at MW-9A, MW-9B, and MW-10A, field specific conductance at MW-10A, sulfate at
<br /> MW-9A, field temperature at MW-9A, MW-9B, and MW-10A, and TDS at MW-10A. The
<br /> 0 chloride concentrations (with high specific conductance values) could indicate a saltwater
<br /> intrusion to the groundwater. The French Camp Landfill is within the central Stockton area
<br /> impacted by saltwater intrusion (Fourth Quarter/Annual 1999 Monitoring Report, French Camp
<br /> Landfill, CH2MHILL,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 and summary tables of the Sen's Slope analyses
<br /> are included in Appendix E.
<br /> Bicarbonate at MW-7A, chloride at MW-10A, potassium at MW-7A and MW-9B, field specific
<br /> conductance at MW-10A, and sulfate at MW-9B exhibited increasing trends, but did not exceed
<br /> their respective concentration limits. Sen's Slope analysis identified decreasing trends in the
<br /> following constituents: calcium at MW-6A and MW-8A, chloride at MW-7A, magnesium at
<br /> MW-8A, nitrate at MW-8A and MW-10A, field pH at MW-6A, MW-8A, MW-9B, and MW-
<br /> 10A, sodium at MW-8A, field specific conductance at MW-7A, sulfate at MW-7A, total
<br /> dissolved solids at MW-7A,and field turbidity at MW-6A,MW-7A, MW-9A, and MW-10A. As
<br /> noted above, MW-6A and MW-7A are background monitoring wells, and trends in the
<br /> groundwater quality at these wells are not indicative of an impact from the facility.
<br /> Chloride at MW-10A, potassium at MW-9B, and field specific conductance at MW-1 OA are the
<br /> only constituents that exceeded their concentration limits and exhibited significant increasing
<br /> statistical trends. The third quarter 2009 concentration of chloride at MW-l0A (600 mg/L) is
<br /> comparable to concentrations observed at that well intermittently since April 2002. The third
<br /> quarter 2009 concentration of potassium at MW-9B (4.1 mg/L) is comparable to concentrations
<br /> observed at that well since May 2007. The third quarter 2009 field specific conductance value at
<br /> MW-l0A (3,230 umhos/cm) is comparable to values observed at that well intermittently since
<br /> March 1997.
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