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from samples collected at the corrective action wells are used to evaluate improvements in
<br /> groundwater quality as a result of previously implemented corrective action measures. •
<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 first quarter
<br /> 2006 monitoring event. Bryan A. Stirrat did not report a field turbidity result for monitoring
<br /> wells AMW-12 or AMW-13 during the first quarter 2006. The field and laboratory results
<br /> provided by BC Laboratories, Inc. for the first quarter 2006 detection monitoring sampling are
<br /> summarized on Table 2.2. The historical groundwater data for the detection monitoring wells are
<br /> presented in Appendix D. The data are graphed on time series concentration plots, included in
<br /> Appendix E. For VOCs, only those compounds that exhibited detections for the first quarter
<br /> 2006 monitoring event were plotted. The concentration limits presented on Table 2.2 were
<br /> calculated by Herst & Associates, Inc. from data collected through the first quarter 2006
<br /> monitoring event. The statistical analysis calculations for detection monitoring wells are included
<br /> in Appendix E. A copy of the statistical analysis methodology is included in Appendix C.
<br /> During the first quarter 2006 monitoring event, barium at AMW-12 and AMW-13, carbonate at
<br /> AMW-7, and field temperature at AMW-6 and AMW-7 exceeded their respective concentration
<br /> limits. Field pH at -7 exhibited a value outside its limit range during the first quarter 2006
<br /> monitoring event. The first quarter 2006 barium concentration at AMW-12 (0.26 mg/L) is
<br /> comparable to concentrations observed at that well since August 2003. The first quarter 2006
<br /> barium concentration at -13 (0.26 mg/L) is comparable to concentrations observed at that
<br /> well since May 1995. The first quarter 2006 barium concentrations at AMW-12 and AMW-13
<br /> are well below the National Primary Drinking Water Standard (2 mg/L). The first quarter 2006
<br /> carbonate concentration at AMW-7 (8 mg/L) is comparable to concentrations observed at that
<br /> well intermittently since March 1994. The first quarter 2006 field temperature values at AMW-6
<br /> (23°C)and AMW-7 (24°C) are comparable to values observed at those wells intermittently since
<br /> June 1996. The first quarter 2006 field pH value at AMW-7 (8.4) is comparable to values
<br /> observed at that well intermittently since April 1995. The first quarter 2006 field pH value at
<br /> AMW-7 is within the National Secondary Drinking Water Standard range(6.5-8.5).
<br /> During the first quarter 2006 monitoring event,no VOCs were detected above the laboratory PQL
<br /> in samples collected from detection monitoring wells AMW-2, AMW-6, AMW-7, or AMW-12.
<br /> 1,1-Dichloroethane, cis-1,2-dichloroethene, dichlorodifluoromethane, tetrachloroethene,
<br /> trichloroethene,and trichlorofluoromethane were detected above the PQL at AMW-13 during the
<br /> first quarter 2006 monitoring event. 1,1-Dichloroethane, dichlorodifluoromethane,
<br /> tetrachloroethene, and trichloroethene were detected above the PQL at AMW-14 during the first
<br /> quarter 2006 monitoring event.
<br /> The first quarter 2006 concentration of 1,1-dichloroethane at AMW-13 (1.1 ug/L) is comparable
<br /> to concentrations observed at that well intermittently since April 1995. The first quarter 2006
<br /> concentration of cis-1,2-dichloroethene at AMW-13 (2.3 ug/L) is the second-highest •
<br /> concentration observed at that well since April 1995, the highest occurring in February 2005 (3.2
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