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The third quarter 2007 concentration of tetrachloroethane at AMW-6 (0.67 ug/L) is slightly • higher than concentrations previously observed at that well, but remains well below the National Primary Drinking Water Standard (5 ug/L). The third quarter 2007 concentration of tetrachlorothene at AMW-13 (1.7 ug/L) is comparable to concentrations observed at that well intermittently since March 1994, and is below the National Primary Drinking Water Standard (5 ug/L). The third quarter 2007 concentration of tetrachloroethene at AMW-14 (7.6 ug/L) is comparable to concentrations observed at that well intermittently since March 1996. The third quarter 2007 concentration of trichloroethene at AMW-14 (0.82 ug/L) is comparable to concentrations observed at that well intermittently since March 1996, and is below the National Primary Drinking Water Standard(5 ug/L). Historical data from the detection monitoring wells were analyzed for temporal trend using Sen's Slope trend analysis. Graphs of the Sen's Slope analyses for detection monitoring wells are included in Appendix E. The following inorganic constituents exhibited an increasing trend according to the Sen's Slope analysis: barium at AMW-6 and AMW-14,bicarbonate at AMW-6, AMW-7, AMW-12, and AMW-13, calcium at AMW-14, chloride at AMW-6 and AMW-7, magnesium at AMW-14, nitrate at AMW-2, AMW-6, and AMW-7, potassium at AMW-14, sodium at AMW-14, field specific conductance at AMW-2 and AMW-7, strontium at AMW-14, and total dissolved solids(TDS)at AMW-7. None of the constituents that exhibited a statistically significant increasing trend during the third quarter 2007 exceeded a concentration limit. Although there were increasing trends for nitrate at AMW-6 and AMW-7 and field specific conductance at AMW-7,background well AMW-2 also exhibited increasing trends for nitrate and field specific conductance during the third quarter 2007 monitoring event. Sen's Slope analysis identified decreasing trends in the following inorganic parameters: arsenic at AMW-2 and AMW-6, calcium at AMW-12, chloride at AMW-12, magnesium at AMW-12, nitrate at AMW-13, field specific conductance at AMW-14, strontium at AMW-12, total dissolved solids(TDS)at AMW-14,and field turbidity at AMW-2. Of the organic constituents that were detected in detection monitoring wells during the third quarter 2007 monitoring event, none exhibited an increasing trend according to the Sen's Slope analysis. Tetrachloroethene and trichloroethene at AMW-14 exhibited statistically significant decreasing trends according to the Sen's Slope analysis. 2.2 Corrective Action Monitoring Groundwater samples were collected by ATC Associates, Inc. from the corrective action monitoring wells (AMW-1, AMW-4, AMW-5R, AMW-10, AMW-11, AMW-18, and AMW-19) during the third quarter 2007 monitoring event. Corrective action monitoring well AMW-5R is a replacement for corrective action monitoring well AMW-5. ATC Associates, Inc. reported that corrective action monitoring well AMW-3 has been abandoned. The field and laboratory results provided by BC Laboratories, Inc. for the third quarter 2007 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-5/5R, AMW-18, and AMW-19 have previously exhibited sporadic VOC detections. 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. 3