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Of the organic parameters that were detected above the laboratory PQL in detection monitoring wells during the fourth quarter 2006 monitoring event, only tetrachloroethene at AMW-13 exhibited an increasing trend according to the Sen's Slope analysis. The fourth quarter 2006 concentration of tetrachlorothene at AMW-13 (1.5 ug/L) is comparable to concentrations observed at that well intermittently since March 1994. The tetrachloroethene concentration at AMW-13 is below the National Primary Drinking Water Standard (5 ug/L). Tetrachloroethene and trichloroethene at AMW-14 exhibited a statistically significant decreasing trend according to the Sen's Slope analysis. Piper diagrams of the first through fourth quarter 2006 results for the detection monitoring wells are included in Appendix H. Hydrographs of the detection monitoring wells, illustrating historic groundwater elevations, well screen elevations, and pump intake elevations, are included in Appendix I. 2.2 Corrective Action Monitoring Groundwater samples were collected by Bryan A. Stirrat & Associates from the corrective action monitoring wells (AMW-1, AMW-4, AMW-10, AMW-11, AMW-18, AMW-19) during the fourth quarter 2006 monitoring event. Bryan A. Stirrat reported that corrective action monitoring well MW -3 has been destroyed, and that corrective action monitoring well MW -5 could not be sampled during the fourth quarter 2006 due to a nonfunctional pump lodged in the well. The field and laboratory results provided by BC Laboratories, Inc. for the fourth 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, AMW-18, and AMW-19 have 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 fourth 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: barium at AMW- 1, AMW-10, and AMW-18, 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 AMW-1, AMW-3, AMW-5, and AMW-10, sulfate at AMW-5 and AMW-10, and total dissolved solids (TDS) at AMW-5. The fourth quarter 2006 concentration of barium at AMW-1 (0.43 mg/L) is higher than concentrations previously observed at that well, but is well below the National Primary Drinking Water Standard (2 mg/L). The fourth quarter 2006 concentration of barium at AMW-10 (0.32 mg/1) is comparable to concentrations observed at that well intermittently since August 2004, and is well below the National Primary Drinking Water Standard (2 mg/L). The fourth quarter 2006 concentration of barium at AMW-18 (0.18) is comparable to concentrations observed at that well 0 4