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MW-9B, and MW-l0A) during the first quarter 2012 monitoring event. The analytical results from samples collected at these wells are used to determine potential landfill-related impacts. The WDRs stipulate semi-annual sampling of the background monitoring wells and detection monitoring wells for field parameters (pH, specific conductance, temperature, and turbidity) and monitoring parameters (bicarbonate,calcium, carbonate, chloride,magnesium, nitrate, potassium, sodium, sulfate,TDS,and VOCs). The field results provided by Del-Tech and the laboratory results provided by BC Labs for the first quarter 2012 groundwater monitoring event are summarized on Table 2.2. The historical groundwater data for the background and detection monitoring wells are presented in Appendix D. Times series concentration plots of historical groundwater data for the monitoring wells are presented in Appendix E. The concentration limits presented on Table 2.2 were calculated from background data collected through the first quarter 2012 monitoring event. The statistical analysis calculations for groundwater monitoring wells are presented in Appendix E. A copy of the statistical analysis methodology is presented in Appendix C. As presented on Table 2.2, the following constituents exceeded their respective concentration limits during the first quarter 2012 event: calcium at MW-913 and MW-10A; chloride at MW-913 and MW-10A; magnesium at MW-10A; and field temperature at MW-913 and MW-10A. There were two VOCs detected at groundwater monitoring wells during the first quarter 2012 event. Chloroform was detected at upgradient well MW-6A at a concentration of 2.8 ug/L, and trichlorofluoromethane was detected at downgradient well MW-9A at a concentration of 2.5 ug/L. Historical data from the groundwater 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 groundwater monitoring wells are presented in Appendix E. Chloride at MW-10A,potassium at MW-913, sulfate at MW-913, and field temperature at MW-8A exhibited significant increasing statistical trends. None of these constituents exceeded their concentration limits. Mann-Kendall / Sen's Slope analysis identified significant decreasing statistical trends in the following constituents: bicarbonate alkalinity at MW-8A; calcium at MW- 6A; chloride at MW-7A and MW-8A; magnesium at MW-6A and MW-8A; nitrate at MW-8A, MW-9A, and MW-10A; field pH at MW-6A and MW-913; field specific conductance at MW-7A; TDS at MW-7A and MW-8A; trichlorofluoromethane at MW-9A; and field turbidity at MW-7A. Given that field pH exhibits a significant decreasing statistical trend at upgradient well MW-6A, the decreasing trend for field pH at downgradient well MW-913 is likely due to ongoing changes in the natural groundwater geochemistry at the site. The first quarter 2012 calcium concentration at well MW-9B (150 mg/L) is within the range of concentrations observed at MW-913 since the beginning of background in May 2005 (109 mg/L - 180 mg/L). As discussed above, calcium at MW-913 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-913 (a= 0.05)indicates that the calcium data at MW-913 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-913 that are statistically distinct from background indicates that the concentration limit exceedance for calcium at MW-913 in the first quarter 2012 is likely due to spatial variation in the natural groundwater geochemistry at the site. The first quarter 2012 calcium concentration at well MW-10A (170 mg/L) is within the range of concentrations observed at MW-l0A since the beginning of background in May 2005 (5 3.5 mg/L - 210 mg/L). As discussed above, calcium at MW-l0A does not exhibit a significant upward