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During the first quarter 2006 monitoring event, analysis for field parameters (pH, specific
<br /> conductance, temperature, and turbidity) and monitoring parameters (barium, bicarbonate,
<br /> calcium, carbonate, chloride, magnesium, nitrate, potassium, sodium, sulfate, and total dissolved
<br /> solids [TDS]) was performed for the background monitoring wells, detection monitoring wells,
<br /> and evaluation monitoring wells.
<br /> 2.1 Results for Detection Monitoring Wells
<br /> First quarter 2006 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 first quarter 2006 '
<br /> detections in background or detection monitoring wells were plotted. The concentration limits
<br /> were developed using data collected through the first quarter 2006. 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: barium at MW-9B, bicarbonate at MW-9A, calcium at MW-9A, MW-9B, and MW-10A,
<br /> chloride at MW-9B and MW-10A, nitrate at MW-9A, potassium at MW-9B, specific
<br /> conductance at MW-10A, sulfate at MW-8A and MW-9A, temperature at MW-9A, MW-9B, and
<br /> MW-10A,and total dissolved solids (TDS)at MW-9B. Monitoring well MW-8A exhibited a pH
<br /> value higher than the concentration limit range. 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, 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. Two constituent both exceeded their concentration limits and exhibited increasing
<br /> trends according to Sen's Slope analysis: chloride and specific conductance at MW-10A. The
<br /> following constituents exhibited an increasing trend but did not exceed their respective
<br /> concentration limits: barium at MW-6A, specific conductance at MW-8A,and sulfate at MW-9B.
<br /> Sen's Slope analysis identified decreasing trends in the following constituents: nitrate at MW-8A
<br /> and MW-10A, pH at MW-6A, sulfate at MW-7A, and turbidity at MW-6A, MW-7A, MW-9A,
<br /> and MW-10A. As noted above, MW-6A and MW-7A are background monitoring wells, and
<br /> trends in the groundwater quality at these wells are not indicative of an impact from the facility.
<br /> Table 2.2 presents the VOC detections at background and detection monitoring wells during the '
<br /> first quarter 2006 monitoring event. 1,2-Dichloroethane was detected in detection monitoring
<br /> well MW-9B at a concentration (0.50 ug/L) that was equal to the reporting limit. 1,2-
<br /> Dichloroethane did not exhibit an increasing trend according to Sen's Slope analysis.
<br /> 2.3 Results for Evaluation Monitoring Wells
<br /> Groundwater samples were collected during the first quarter 2006 monitoring event from
<br /> evaluation monitoring wells MW-IA and MW-2. The field and laboratory results from the first
<br /> quarter 2006 sampling event are summarized on Table 2.3. The historical groundwater data for
<br /> the evaluation monitoring wells are presented in Appendix F. The field and monitoring
<br /> parameter data are presented on time series concentration plots in Appendix G. For VOCs, only
<br /> those VOCs with first quarter 2006 detections in evaluation monitoring wells were plotted.
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