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2.2 Corrective Action Monitoring Groundwater samples were collected by Bryan A. Stirrat & Associates from the corrective action • monitoring wells (AMW-1, AMW-3, AMW-4, AMW-10, and AMW-11) during the first quarter 2006 monitoring event. Corrective action monitoring well AMW-5 was not sampled during the first quarter 2006 monitoring event. Bryan A. Stirrat & Associates reported that the sample at AMW-5 was not collected due to a nonfunctional pump. The field and laboratory results provided by BC Laboratories, Inc. for the first quarter 2006 corrective action sampling are summarized on Table 2.3. VOCs have been consistently detected in samples from corrective action monitoring wells AMW- 1, AMW-4, AMW-10, and AMW-11. AMW-5 has previously exhibited sporadic VOC detections. No VOCs have been detected in samples from AMW-3 since 1990. The historical groundwater data for the corrective action monitoring wells are presented in Appendix F. The data are graphed on time series concentration plots, included in Appendix G. For VOCs, only those VOCs that exhibited detections for the first quarter 2006 monitoring event were plotted. Historical data from the corrective action monitoring wells from March 1994 to the present were analyzed for temporal trend using Sen's Slope trend analysis. Graphs of the Sen's Slope analyses for corrective action monitoring wells are included in Appendix G. Table 2.4 summarizes the results of the corrective action monitoring well trend analysis. The following inorganic constituents exhibited an increasing trend according to the Sen's Slope analysis: bicarbonate at AMW-1,chloride at AMW-3 and AMW-5, nitrate at AMW-3 and AMW-5, field pH at AMW-5, field specific conductance at -1, AMW-3, AMW-5, and AMW-10, sulfate at AMW-5 and AMW-10,and total dissolved solids(TDS)at AMW-5. The first quarter 2006 concentration of bicarbonate at AMW-1 (1100 mg/L) is comparable to concentrations observed at that well intermittently since February 2004. The first quarter 2006 concentration of chloride at AMW-3 (100 mg/L)is comparable to concentrations observed at that well consistently since August 2003, and is below the National Secondary Drinking Water Standard (250 mg/L). The first quarter 2006 concentration of nitrate at AMW-3 (17 mg/L) is comparable to concentrations observed at that well consistently since August 2004. The first quarter 2006 nitrate concentration at AMW-3 is less than the first quarter 2006 nitrate concentration at background detection monitoring well AMW-2 (38 mg/L). The first quarter 2006 field specific conductance value at AMW-1 (1,300 umhos/cm) is comparable to values observed at that well consistently since March 2003. The first quarter 2006 field specific conductance value at AMW-3 (1,600 umhos/cm) is the highest value observed at that well since March 1994. The first quarter 2006 field specific conductance value at AMW-10 (960 umhos/cm) is the lowest value observed at that well since February 2004. The first quarter 2006 field specific conductance values at AMW-1 and AMW-10 are both less than the first quarter 2006 field specific conductance value at background detection monitoring well AMW-2 (1,500 umhos/cm). The first quarter 2006 concentration of sulfate at AMW-10(61 mg/L) is comparable to concentrations observed at that well for the last five monitoring events, and is well below the National Secondary Drinking Water Standard (250 mg/L). The first quarter 2006 concentration of sulfate at AMW-10 is less than the first quarter 2006 sulfate concentration at background detection monitoring well AMW-2(120 mg/L). Sen's Slope analysis identified decreasing trends in the following inorganic parameters: arsenic at • AMW-3, calcium at AMW-11, chloride at AMW-1, AMW-4, and AMW-11, magnesium at 4