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fourth quarter 2012 is likely due to spatial variation in the natural groundwater geochemistry at the site. The fourth quarter 2012 field temperature value at AMW-7 (21.3 °C) is within the range of values observed at that well since the beginning of monitoring in March 1994 (16.9 to 24 °C). As discussed above, temperature at AMW-7 does not exhibit a significant increasing statistical trend. A Wilcoxon rank -sum test comparing the temperature data at upgradient well AMW-2 to the data at AMW-7 (a = 0.05) indicates that the temperature 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 temperatures at AMW-7 that are statistically distinct from upgradient temperatures indicates that the exceedance for temperature at AMW-7 in the fourth quarter 2012 is likely due to spatial variation in the natural groundwater temperatures at the site. The fourth quarter 2012 concentration of dichlordifluoromethane at AMW-13 (7.8 ug/L) is within the range of concentrations observed at that well since the beginning of monitoring in April 1995 (<O.18 to 130 ug/L), but is above the California Department of Public Health's Notification Level of 1 ug/L. There is no established National Primary Drinking Water Standard for dichlorodifluoromethane. However, as discussed above, dichlorodifluoromethane at AMW-13 does not exhibit a significant increasing statistical trend. The fourth quarter 2012 concentration of tetrachloroethene at AMW-13 (0.5 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, tetrachloroethane at AMW-13 does not exhibit a significant increasing statistical trend. The fourth quarter 2012 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 in 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 fourth quarter 2012 concentration of tetrachloroethene at AMW-14 (0.86 ug/L) is within the range of concentrations observed at that well since the beginning of monitoring in 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 exhibits a significant decreasing statistical trend. 2.2 Corrective Action Monitoring During the fourth quarter 2012 monitoring event, Del -Tech collected groundwater samples from corrective action monitoring wells (AMW-1, AMW-4, AMW-5R, AMW-10, AMW-11, AMW- 18, AMW-19, and AMW-19BR). Corrective action monitoring well AMW-5R is a replacement for corrective action monitoring well AMW-5. Corrective action monitoring well AMW-19BR is a replacement for corrective action monitoring well AMW-19B. The field results provided by Del -Tech and laboratory results provided by BC Labs for the fourth quarter 2012 corrective action monitoring event are summarized on Table 2.3. The historical groundwater data for the corrective action monitoring wells are presented in Appendix F. Times series concentration plots of historical groundwater data for the detection monitoring wells are presented in Appendix G. For VOCs, only those compounds that exhibited detections at corrective action monitoring wells during the fourth quarter 2012 monitoring event were plotted. During the fourth quarter 2012, there were no VOCs detected above the laboratory RL in wells AMW-4, AMW-5R, AMW-11, AMW-18, or AMW-19. 1,1-Dichloroethane, 1,4-