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The Wilcoxon rank sum plot is presented in Appendix E. The presence of stable hexavalent chromium concentrations at AMW-6 that are statistically distinct from upgradient concentrations indicates that the concentration limit exceedance for hexavalent chromium at AMW-6 in the first quarter 2012 is likely due to spatial variation in the natural groundwater geochemistry at the site. The first quarter 2012 hexavalent chromium at AMW-7 (0.0057 mg/L) is within the range of concentrations observed at that well since the beginning of monitoring in July 1995 (<0.002 to 0.01 mg/L). As discussed above, hexavalent chromium at AMW-7 does not exhibit a significant increasing statistical trend. A Wilcoxon rank-sum test comparing the hexavalent chromium data at upgradient well AMW-2 to the data at AMW-7 (a = 0.05) indicates that the hexavalent chromium data at AMW-7 are statistically distinct from those at the upgradient well. The Wilcoxon rank sum plot is presented in Appendix E. The presence of stable hexavalent chromium concentrations at AMW-7 that are statistically distinct from upgradient concentrations indicates that the concentration limit exceedance for hexavalent chromium at AMW-7 in the first quarter 2012 is likely due to spatial variation in the natural groundwater geochemistry at the site. The first quarter 2012 concentration of dichlorodifluoromethane at AMW-13 (0.63 ug/L) is within the range of concentrations observed that well since the beginning of monitoring in April 1995 (<0.18 to 130 ug/L). As discussed above, dichlorodifluoromethane at AMW-13 does not exhibit a significant increasing statistical trend. The first quarter 2012 concentration of tetrachloroethene at AMW-13 (9.6 ug/L) is within the range of concentrations observed at that well since the beginning of monitoring in October 1991 (<0.21 to 43 ug/L), but is above the National Primary Drinking Water Standard of 5 ug/L. However, as discussed above, tetrachloroethene at AMW-13 does not exhibit a significant increasing statistical trend. The first quarter 2012 concentration of trichloroethene at AMW-13 (2.7 ug/L) is within the range of concentrations observed at that well since the beginning of monitoring October 1991 (0.17 to 15 ug/L), and is below the National Primary Drinking Water Standard of 5 ug/L. As discussed above, trichloroethene at AMW-1 3 does not exhibit a significant increasing statistical trend. The first quarter 2012 concentration of trichlorofluoromethane at AMW-13 (0.53 ug/L) is within the range of concentrations observed at that well since the beginning of monitoring October 1991 (<0.07 to 1.4 ug/L), and is below the National Primary Drinking Water Standard of 5 ug/L. As discussed above, trichlorofluoromethane at AMW-13 does not exhibit a significant increasing statistical trend. The first quarter 2012 concentration of tetrachloroethene at AMW-14 (1.5 ug/L) is within the range of concentrations observed at that well since the beginning of monitoring July 1995 (<0.21 to 100 ug/L), and is below the National Primary Drinking Water Standard of 5 ug/L. As discussed above,tetrachloroethene at AM -14 does not exhibit a significant increasing statistical trend. 2.2 Corrective Action Monitoring During the first quarter 2012 monitoring event, Del-Tech collected groundwater samples from corrective action monitoring wells (AMW-1, AMW-4, AMW-5R, AMW-10, AMW-1 1, AMW- 18, AMW-19, and AMW-19BR). Corrective action monitoring well AMW-5R is a replacement for corrective action monitoring well AMW-5. Corrective action monitoring well AMW-19BR is a replacement for corrective action monitoring well AMW-1913. The field results provided by Del-Tech and laboratory results provided by BC Labs for the first quarter 2012 corrective action monitoring event are summarized on Table 2.2. The historical groundwater data for the corrective action monitoring wells are presented in Appendix F. Times series concentration plots of historical groundwater data for the detection monitoring wells are presented in Appendix G. 4