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2.0 Groundwater Monitoring
<br /> Groundwater samples were collected by ATC Associates, Inc. during the third quarter 2007
<br /> monitoring event from the detection monitoring and corrective action wells at the site.
<br /> Monitoring well AMW-2, which is upgradient from the landfill, is the designated background
<br /> well. Monitoring wells AMW-6, AMW-7, AMW-12, AMW-13, and AMW-14 are currently
<br /> designated as detection monitoring wells. Monitoring wells AMW-1, AMW-3, AMW-4, AMW-
<br /> 5R, AMW-10,AMW-11, AMW-18, and AMW-19 are designated as corrective action monitoring
<br /> wells. Corrective action monitoring well AMW-5R is a replacement for corrective action
<br /> monitoring well AMW-5. The analytical results from samples collected at the corrective action
<br /> wells are used to evaluate improvements in groundwater quality as a result of previously
<br /> implemented corrective action measures.
<br /> ATC Associates, Inc. reported that corrective action monitoring well AMW-3 has been
<br /> abandoned.
<br /> Groundwater samples are scheduled to be analyzed quarterly for field parameters (groundwater
<br /> elevation, pH, specific conductance, temperature, and turbidity) and monitoring parameters
<br /> (arsenic, barium, bicarbonate, calcium, carbonate, chloride, gasoline-range petroleum
<br /> hydrocarbons, hexavalent chromium, magnesium, nitrate, oil and grease, potassium, sodium,
<br /> strontium, sulfate,TDS, and VOCs).
<br /> 2.1 Detection Monitoring
<br /> Groundwater samples were collected from the background well (AMW-2) and detection
<br /> monitoring wells (AMW-6, AMW-7, AMW-12, AMW-13, and AMW-14) during the third
<br /> quarter 2007 monitoring event. The field and laboratory results provided by BC Laboratories,
<br /> Inc. for the third quarter 2007 detection monitoring sampling are summarized on Table 2.2. The
<br /> historical groundwater data for the detection monitoring wells are presented in Appendix D. The
<br /> data are graphed on time series concentration plots, included in Appendix E. For VOCs, only
<br /> those compounds that exhibited detections for the third quarter 2007 monitoring event were
<br /> plotted. The concentration limits presented on Table 2.2 were calculated by Herst & Associates,
<br /> Inc. from data collected through the third quarter 2007 monitoring event. The statistical analysis
<br /> calculations for detection monitoring wells are included in Appendix E. A copy of the statistical
<br /> analysis methodology is included in Appendix C.
<br /> During the third quarter 2007 monitoring event, barium at AMW-13, carbonate at AMW-7, and
<br /> hexavalent chromium at AMW-7 exceeded their respective concentration limits. The third
<br /> quarter 2007 barium concentration at AMW-13 (0.27 mg/L) is comparable to concentrations
<br /> observed at that well since May 1995, and is well below the National Primary Drinking Water
<br /> Standard (2 mg/L). The third quarter 2007 carbonate concentration at AMW-7 (13 mg/L) is
<br /> comparable to concentrations observed at that well intermittently since August 1991. The third
<br /> quarter 2007 hexavalent chromium concentration at AMW-7 (0.0078 mg/L) is comparable to
<br /> concentrations observed at that well intermittently since August 2003, and is well below the
<br /> National Primary Drinking Water Standard for chromium(0.1 mg/L).
<br /> During the third quarter 2007 monitoring event, no VOCs were detected above the laboratory
<br /> PQL in samples collected from detection monitoring wells AMW-7 or AMW-12.
<br /> Tetrachloroethene was detected above the PQL at AMW-6 and AMW-13 during the third quarter
<br /> ® 2007. Tetrachloroethene and trichloroethene were detected above the PQL at AMW-14 during
<br /> the third quarter 2007.
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