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April 2014 10 10381640A 4.0 RESULTS AND DISCUSSION 4.1 Water Chemistry Data In addition to the groundwater monitoring described in Section 2.4, Golder has performed quarterly monitoring of wells MW -5, MW -6 and MW -7 since the first quarter of 2013. Analytical results for all groundwater monitoring events are presented in Table 3 through Table 9. In 2010, benchmarks levels were established for each constituent analyzed from the eight samples collected from MW -2, MW -3, and MW -4 collected from April 1999 through July 2000. The methods are described in the Groundwater SAP for the Boettcher Limestone Quarry (Golder 2010). In summary, benchmarks were determined either from: 1. Regulatory standards listed in the Colorado Department of Public Health and Environment (CDPHE) Regulation 41, Basic Standards for Groundwater Tables 1 through 4 (Regulations); or 2. Intra -well statistical methods performed on background concentrations from April 1999 through July 2000. A detailed description of the methods used for determining benchmark levels was presented in the Golder 2010 Groundwater SAP. Observed constituent trends and benchmark exceedances for the wells with established benchmark levels (MW -2, MW -3 and MW -4) are summarized below. For the wells without established benchmark levels (MW -1, MW -5, MW -6, and MW -7), the constituent concentrations are described relative to the other wells. A piper diagram depicting the major ion chemistry for the groundwater samples is presented in Figure 4. Concentration verses time plots for the entire data period (April 1999 to present) are presented in Appendix D. The analyte list has been periodically modified since sampling began in April 1999, and the discussion below only includes the 2013 analyte suite. 4.1.1 Monitoring Well MW -1 Monitoring well MW -1 is located near the western edge of CKD disposal area A2 (Figure 1). Benchmark analyte levels were not determined for well MW -1; however, constituent concentrations from MW -1 were used to help evaluate the constituent concentrations from the hydraulically downgradient wells. Groundwater samples collected from MW -1 are predominantly sodium - sulfate type waters (Figure 4). The samples exhibited higher concentrations of dissolved calcium and magnesium but lower chloride and alkalinity concentrations than those of the other Site wells (Appendix D). The MW -1 samples have pH values ranging from 7.3 to 8.2, and remain consistent with values observed prior to CKD material placement in disposal area A2. The MW -1 samples exhibited higher TDS concentrations than Golder i.ti0t 1640a� \ h iiin llfi r fnl- r 4 \1 1 Associates 8 0400 gwc arwe sla eld ep_ 30ap 1 038 640a gvcharrpt_holcim- bcettcher _ fnl- 28apria- with holcim edits