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localized change in the site's natural geochemistry near AMW-14 in 2009. This change was signified by a shift in barium at AMW-14 to higher but stable concentrations. The fourth quarter 2012 chloride concentration at AMW-12 (87 mg/L) is within the range of concentrations observed at that well since the beginning of monitoring in August 1991 (24 to 90 mg/L). As discussed above, chloride at AMW-12 does not exhibit a significant increasing statistical trend when the entirety of the August 1991 through November 2012 data set is considered. A Wilcoxon rank -sum test comparing the chloride data at upgradient well AMW-2 to the data at AMW-12 (a = 0.05) indicates that the chloride data at AMW-12 are not statistically distinct from those at the upgradient well. The Wilcoxon rank sum plot is presented in Appendix E. The presence of stable chloride concentrations at AMW-12 that are not statistically distinct from upgradient concentrations indicates that the concentration limit exceedance for chloride at AMW-12 in the fourth quarter 2012 is likely due to variation time in the natural groundwater geochemistry near AMW-12. Examination of the time series plot for chloride at AMW-12 indicates that chloride concentrations generally decreased to a low of 24 mg/L in May 2003, then began to increase, and have since stabilized in the past two years. An increasing trend is observed when the data are limited to the period of May 2003 through November 2012, but no trend is observed when the data are limited to the period of June 2010 through November 2012. The fourth quarter 2012 chloride concentration at AMW-14 (81 mg/L) is within the range of concentrations observed at that well since the beginning of monitoring in July 1995 (3 to 168 mg/L). As discussed above, chloride at AMW-14 exhibits a significant increasing statistical trend. The increasing trend is not observed when the data are limited to the period of March 2010 to November 2012. A Wilcoxon rank -sum test comparing the July 1995 to November 2009 chloride data at -14 to the March 2010 to November 2012 data data (a = 0.05) indicates that these periods are statistically distinct. The Wilcoxon rank sum plot is presented in Appendix E. This indicates that the significant increasing statistical trend in chloride at AMW-14 may be due to a localized change in the site's natural geochemistry near AMW-14 in 2009-2010. This change was signified by a shift in chloride at AMW-14 to higher but stable concentrations. The fourth quarter 2012 hexavalent chromium concentration at AMW-6 (0.0051 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 at AMW-6 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 fourth quarter 2012 is likely due to spatial variation in the natural groundwater geochemistry at the site. The fourth quarter 2012 hexavalent chromium concentration at AMW-7 (0.0058 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