ARCHIVED REPORTS_2011_12 - Laserfiche WebLink

Home Browse Search

Given that bicarbonate alkalinity, nitrate, and field specific conductance exhibit significant increasing trends at upgradient well AMW-2, the increasing trends for these constituents at downgradient wells are likely due to ongoing changes in the natural groundwater geochemistry at the site. Mann-Kendall / Sen's Slope analysis identified significant decreasing statistical trends in the following inorganic constituents: barium at AMW-12, calcium at AMW-12, chloride at AMW- 12, magnesium at AMW-12, nitrate at AMW-13, potassium at AMW-7, strontium at AMW-12, and field turbidity at AMW-2. Mann-Kendall / Sen's Slope analysis did not identify any significant increasing statistical trends for VOCs. Mann-Kendall / Sen's Slope analysis identified significant decreasing statistical trends for tetrachloroethene and trichloroethene at AMW-14. The first quarter 2011 barium concentration at AMW-13 (0.25 mg/L) is within the range of concentrations observed at AMW-13 since the beginning of monitoring in May 1995 (0.24 to 0.34 mg/L). As discussed above, barium at AMW-13 does not exhibit a significant increasing statistical trend. A Wilcoxon rank-sum test comparing the barium data at upgradient well AMW- 2 to the data at AMW-13 (a = 0.05) indicates that the barium data at AMW-13 are statistically distinct from those at the upgradient well. The Wilcoxon rank sum plot is presented in Appendix E. The presence of stable barium concentrations at AMW-13 that are statistically distinct from upgradient concentrations indicates that the concentration limit exceedance for barium at AMW- 13 in the first quarter 2011 is likely due to spatial variation in the natural groundwater geochemistry at the site. The first quarter 2011 barium concentration at AMW-14 (0.228 mg/L) is within the range of concentrations observed at AMW-14 since the beginning of monitoring in July 1995 (0.093 to 0.3 mg/L). As discussed above,barium at AMW-14 exhibits a significant increasing statistical trend. The increasing trend is not observed when the data are limited to the period of May 2006 to March 2011. A Wilcoxon rank-sum test comparing the July 1995 to February 2006 barium data at AMW-14 to the May 2006 to March 2011 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 barium at AMW-14 may be due to a localized change in the site's natural geochemistry near AMW-14 in 2006. This change was signified by a shift in barium at AMW-14 to higher but stable concentrations. A Wilcoxon rank-sum test comparing the barium data at upgradient well AMW-2 to the data at AMW-14 from May 2006 to March 2011 (a = 0.05) indicates that the barium data at AMW-14 are statistically distinct from those at the upgradient well. The Wilcoxon rank sum plot is presented in Appendix E. The presence of stable barium concentrations at AMW-14 that are statistically distinct from upgradient concentrations indicates that the concentration limit exceedance for barium at AMW-14 in the first quarter 2011 is likely due to spatial variation in the natural groundwater geochemistry at the site. The first quarter 2011 concentration of tetrachloroethene at AMW-13 (9.7 ug/L) is within the range of concentrations observed at AMW-13 since November 1999(1 to 43 ug/L). As discussed above, tetrachloroethene at AMW-13 does not exhibit a significant increasing statistical trend. The first quarter 2011 concentration of tetrachloroethene at AMW-14 (2.4 ug/L) is within the range of concentrations observed at AMW-14 since March 1996 (0.49 to 100 ug/L). As discussed above,tetrachloroethene at AMW-14 does not exhibit a significant increasing statistical trend. The first quarter 2011 concentration of trichloroethene at AMW-13 (2.2 ug/L)is within the 3