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hydrocarbons, hexavalent chromium, magnesium, nitrate, oil and grease, potassium, sodium, strontium, sulfate,TDS,and VOCs). 2.1 Detection Monitoring During the first quarter 2012 monitoring event, Del-Tech collected groundwater samples from the background well (AMW-2) and detection monitoring wells (AMW-6, AMW-7, AMW-12, AMW-13, and AMW-14). The field results provided by Del-Tech and laboratory results provided by BC Labs for the first quarter 2012 groundwater detection monitoring event are summarized on Table 2.1. The historical groundwater data for the detection monitoring wells are presented in Appendix D. Times series concentration plots of historical groundwater data for the detection monitoring wells are presented in Appendix E. For VOCs, only those compounds that exhibited detections at detection monitoring wells during the first quarter 2012 monitoring event were plotted. The concentration limits presented on Table 2.1 were calculated by Herst & Associates, Inc. from data collected through the first quarter 2012 monitoring event. The statistical analysis calculations for detection monitoring wells are presented in Appendix E. Information on the development of the concentration limits can be found in the Fourth Quarter/Annual 1999 Monitoring Report, Austin Road Landfill, prepared by CH2M Hill in January 2000. A copy of the statistical analysis methodology is presented in Appendix C. As presented on Table 2.1, the following constituents exceeded their respective concentration limits during the first quarter 2012: barium at W-13 and AMW-14; chloride at AMW-14; and hexavalent chromium at AMW-6 and AMW-7. During the first quarter 2012 monitoring event, no VOCs were detected above the laboratory reporting limit (RL) in samples collected from detection monitoring wells AMW-2, AMW-6, AMW-7, or AMW-12. Dichlorodifluoromethane, tetrachloroethene, trichloroethene, and trichlorofluoromethane were detected above the laboratory RL at AMW-13. Tetrachloroethene was detected above the laboratory RL at AMW-14. Historical data from the detection monitoring wells were analyzed for temporal trends using Mann-Kendall / Sen's Slope trend analysis. Graphs and summary tables of the Mann-Kendall / Sen's Slope analyses for detection monitoring wells are presented in Appendix E. For constituents whose historical data consist primarily of non-detects (carbonate alkalinity, oil and grease, volatile petroleum hydrocarbons, and VOCs), trend evaluation was performed on data from the earliest detection through the present. Wells with no historical detections for a constituent were not evaluated for trends. Mann-Kendall / Sen's Slope analysis identified significant increasing statistical trends for the following inorganic constituents: barium AMW-6 and AMW-14; bicarbonate alkalinity at AMW- 2, AMW-7, and AMW-13; calcium at AM -7 and AMW-14; chloride at AMW-6, AMW-7 and AMW-14; hexavalent chromium at AMW-14; magnesium at AMW-6, AMW-7, and AMW-14; nitrate at AMW-2, AMW-6, AMW-7, and AMW-14; potassium at AMW-14; sodium at AMW- 14; field specific conductance at AMW-2, AMW-6, and AMW-7; strontium at AMW-6 and AMW-14; sulfate at AMW-7, AMW-13, AMW-14; and TDS at AMW-6 and AMW-7. Given that bicarbonate alkalinity, nitrate, and field specific conductance exhibit significant increasing trends at upgradient well AM -2, the increasing trends for these constituents at downgradient wells are likely due to ongoing changes in the natural groundwater geochemistry at the site. 2