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statistical trend. A Wilcoxon rank-sum test comparing the calcium data at background wells MW-6A and MW-7A to the data at MW-10A (a= 0.05) indicates that the calcium data at MW- l0A are statistically distinct from those at the background wells. The Wilcoxon rank sum plot is presented in Appendix E. The presence of stable calcium concentrations at MW-10A that are statistically distinct from background indicates that the concentration limit exceedance for calcium at MW-10A in the third quarter 2012 is likely due to spatial variation in the natural groundwater geochemistry at the site. The third quarter 2012 chloride concentration at well MW-l0A (620 mg/L) is within the range of concentrations observed at MW-10A since the beginning of background in March 1997 (50.5 mg/L - 670 mg/L). As discussed above, chloride at MW-10A exhibits a significant upward statistical trend. However, the increasing trend is no observed when the data are limited to the period of February 1999 to September 2012. A Wilcoxon rank-sum test comparing the March 1997 to October 1998 chloride data at MW-10A to the February 1999 to September 2012 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 concentration limit exceedance for chloride at MW-10A is the third quarter 2012 may be to due to a localized change in the site's natural groundwater geochemistry near AMW-10A in 1998-1999. This change was signified by a shift in chloride at MW-l0A to higher but stable concentrations. The third quarter 2012 magnesium concentration at well MW-l0A(I 10 mg/L) is within the range of concentrations observed at MW-10A since the beginning of background in May 2005 (23.8 mg/L - 120 mg/L). As discussed above, magnesium at MW-10A does not exhibit a significant upward statistical trend. A Wilcoxon rank-sum test comparing the magnesium data at background wells MW-6A and MW-7A to the data at MW-10A (a = 0.05) indicates that the magnesium data at MW-10A are statistically distinct from those at the background wells. The Wilcoxon rank sum plot is presented in Appendix E. The presence of stable magnesium concentrations at MW-10A that are statistically distinct from background indicates that the concentration limit exceedance for magnesium at MW-l0A in the third quarter 2012 is likely due to spatial variation in the natural groundwater geochemistry at the site. The third quarter 2012 field specific conductance value at well MW-10A (3,275 umhos/cm) is within the range of conductances observed at MW-10A since the beginning of background in March 1997 (523 umhos/cm to 3,900 umhos/cm). As discussed above, field specific conductance at MW-10A does not exhibit a significant upward statistical trend. A Wilcoxon rank-sum test comparing the field specific conductance data at background wells MW-6A and MW-7A to the data at MW-10A (a = 0.05) indicates that the conductance data at MW-10A are statistically distinct from those at the background wells. The Wilcoxon rank sum plot is presented in Appendix E. The presence of stable field specific conductance values at MW-10A that are statistically distinct from background indicates that the exceedance for field specific conductance at MW-l0A in the third quarter 2012 is likely due to spatial variation in the natural groundwater geochemistry at the site. The third quarter 2012 field temperature value at well MW-8A (23.4 °C) is above the range of temperatures observed at MW-8A since the beginning of background in March 1997 (17.4 °C - 22.9 °C). As discussed above, field temperature at MW-8A exhibits a significant upward statistical trend. However, the increasing trend is not observed when the data are limited to the period of May 2004 to September 2012. A Wilcoxon rank-sum test comparing the March 1997 to February 2004 field temperature data at MW-8A to the May 2004 to September 2012 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 exceedance for field temperature at MW-8A may be due to a localized thermal change near MW-8A in 2004. This change was signified by a shift in field temperatures at MW-8A to higher but stable values.