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Piper diagrams of the first and third quarter 2008 results for the surface water monitoring points
<br /> are included in Appendix F.
<br /> 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-913,
<br /> and MW-l0A) during the third quarter 2008 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 2008 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 2008 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 2008. 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-913 and MW-10A, chloride at MW-913 and MW-10A, magnesium at MW-
<br /> 10A, field pH at MW-9A and MW-10A, potassium at MW-913, field temperature at MW-9A,
<br /> MW-913, and MW-10A, and TDS at MW-10A. The chloride concentrations (with high specific
<br /> conductance values) could indicate a saltwater intrusion to the groundwater. The French Camp
<br /> Landfill is within the central Stockton area impacted by saltwater intrusion (Fourth
<br /> Quarter/Annual 1999 Monitoring Report, French Camp 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 of the Sen's Slope analyses are included in
<br /> Appendix E.
<br /> Bicarbonate at MW-7A, chloride at MW-10A, and sulfate at MW-9B exhibited increasing trends,
<br /> but did not exceed their respective concentration limits. Sen's Slope analysis identified
<br /> decreasing trends in the following constituents: chloride at MW-7A, magnesium at MW-8A,
<br /> nitrate at MW-8A and MW-10A, field pH at MW-6A and MW-913, sodium at MW-8A, field
<br /> specific conductance at MW-7A, sulfate at MW-7A, total dissolved solids at MW-7A, and field
<br /> turbidity at MW-7A, MW-9A, and MW-10A. As noted above, MW-6A and MW-7A are
<br /> background monitoring wells, and trends in the groundwater quality at these wells are not
<br /> indicative of an impact from the facility. Chloride at MW-l0A was the only constituent that
<br /> exceeded its concentration limit and exhibited a significant increasing statistical trend. The third
<br /> quarter 2008 concentration of chloride at MW-l0A (430 mg/L) is comparable to concentrations
<br /> observed at that well since May 2001.
<br /> As presented in Table 2.2, there were three VOCs detected at detection monitoring wells during
<br /> the third quarter 2008 monitoring event. bis(2-Ethylhexyl)phthalate was detected at MW-6A (2.5
<br /> ug/L), MW-7A (2.7 ug/L), MW-8A (2.3 ug/L), MW-9A (2.3 ug/L), MW-913 (2.8 ug/L), and
<br /> MW-l0A (2.9 ug/L) at concentrations that are below the laboratory PQL of 5 ug/L. However,
<br /> bis(2-ethylhexyl)phthalate was also detected in the laboratory method blank at a concentration of
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