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chloride at AMW-14 in the second quarter 2011 is likely due to recent temporal variation in the natural groundwater geochemistry at the site. The second quarter 2011 hexavalent chromium concentration at AMW-6 (0.005 mg/L) is within the range of concentrations observed at that well since the beginning of monitoring in July 1995 (<0.002 to 0.0068 mg/L). As discussed above, hexavalent chromium 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-6 (a = 0.05) indicates that the hexavalent chromium data at AMW-6 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-6 that are statistically distinct from upgradient concentrations indicates that the concentration limit exceedance for hexavalent chromium at AMW-6 in the second quarter 2011 is likely due to spatial variation in the natural groundwater geochemistry at the site. The second quarter 2011 hexavalent chromium concentration 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 second quarter 2011 is likely due to spatial variation in the natural groundwater geochemistry at the site. The second quarter 2011 concentration of tetrachloroethene at AMW-6 (0.9 ug/L) is within the range of concentrations observed at that well since the beginning of monitoring in February 1991 (<O.16 to 7 ug/L), and is below the National Primary Drinking Water Standard of 5 ug/L. As discussed above, tetrachloroethene at AMW-6 does not exhibit a significant increasing statistical trend. The second quarter 2011 concentration of dichlorodifluoromethane at AMW-13 (0.68 ug/L) is within the range of concentrations observed at that well since the beginning of monitoring in April 1995 (<0.18 to 130 ug/L). Dichlorodifluoromethane does not have an established National Primary Drinking Water Standard. As discussed above, dichlorodifluoromethane at AMW-13 does not exhibit a significant increasing statistical trend. The second quarter 2011 concentration of tetrachloroethene at AMW-13 (8.6 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 second quarter 2011 concentration of trichloroethene at AMW- 13 (2.2 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-13 does not exhibit a significant increasing statistical trend. The second quarter 2011 concentration of tetrachloroethene at AMW-14 (1.3 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 AMW-14 0 does not exhibit a significant increasing statistical trend. 4