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The first quarter 2011 calcium concentration at well MW-9B (143 mg/L) is within the range of concentrations observed at MW-9B since the beginning of background in May 2005 (109 mg/L— 180 mg/L). As discussed above, calcium at MW-9B does not exhibit a significant upward statistical trend. A Wilcoxon rank-sum test comparing the calcium data at background wells MW-6A and MW-7A to the data at MW-9B (a=0.05) indicates that the calcium data at MW-9B 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-9B that are statistically distinct from background indicates that the concentration limit exceedance for calcium at MW-9B in the first quarter 2011 is likely due to spatial variation in the natural groundwater geochemistry at the site. The first quarter 2011 chloride concentration at well MW-9B (456 mg/L) is within the range of concentrations observed at MW-913 since the beginning of background in March 1997 (239 mg/l — 585 mg/L). As discussed above, chloride at MW-9B does not exhibit a significant upward statistical trend. A Wilcoxon rank-sum test comparing the chloride data at background wells MW-6A and MW-7A to the data at MW-9B (a=0.05)indicates that the chloride data at MW-9B are statistically distinct from those at the background wells. The Wilcoxon rank sum plot is presented in Appendix E. The presence of stable chloride concentrations at MW-9B that are statistically distinct from background indicates that the concentration limit exceedance for chloride at MW-913 in the first quarter 2011 is likely due to spatial variation in the natural groundwater geochemistry at the site. The first quarter 2011 potassium concentration at well MW-9B (3.7 mg/L) is within the range of concentrations observed at MW-9B since the beginning of background in May 2005 (3.3 mg/L to 40.2 mg/L), and is the lowest concentration observed at that well since February 2007. As discussed above, potassium at MW-9B exhibits a significant upward statistical trend. However, this trend is not observed when the four most recent monitoring events (August 2009, March 2010, August 2010, and February 2011) are excluded. This indicates that the significant upward statistical trend in potassium at MW-9B is due primarily to recent concentration increases. The first quarter 2011 potassium concentration at well MW-9B (3.7 mg/L) is less than a concentration recently observed at background well MW-7A in August 2010 (5.24 mg/L). This indicates that the concentration limit exceedance for potassium at MW-9B in the first quarter 2011 may be due to recent,ongoing changes in the natural groundwater geochemistry at the site. The first quarter 2011 field temperature value at well MW-l0A (23.7 °C) is within the range of temperatures observed at MW-l0A since the beginning of background in March 1997 (13.5 °C - 26.9 °C), and is the lowest temperature observed at that well since February 2009. As discussed above, field temperature at MW-10A does not exhibit a significant upward statistical trend. A Wilcoxon rank-sum test comparing the field temperature data at background wells MW-6A and MW-7A to the data at MW-l0A (a= 0.05) indicates that the field temperature 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 field temperatures at MW-l0A that are statistically distinct from background temperatures indicates that the concentration limit exceedance for field temperature at MW-l0A in the first quarter 2011 is likely due to spatial variation in the natural groundwater temperatures at the site.