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April 2014 13 10381640A <br />The majority of dissolved trace metal concentrations in samples collected from MW-4 are in the range of <br />those of the other Site wells. From September 2010 to present only three of the 16 constituents have <br />exceeded established benchmark concentrations including: <br />■ Barium — The concentration of barium exceeded the established benchmark <br />concentration of 2.0 mg /L during all of the monitoring events with a maximum <br />concentration of 9.22 mg /L. <br />• Iron — The concentration of iron exceeded the established benchmark concentration of <br />0.61 mg /L during three of the 13 monitoring events with a maximum concentration of 1.1 <br />mg /L. During the benchmark statistical analysis a potential outlier with a concentration of <br />1.13 mg /L was identified and subsequently removed. Inclusion of the potential outlier in <br />the statistical analysis would have resulted in a higher benchmark level. <br />• TDS — The concentration of TDS exceeded the established benchmark concentration of <br />10,212 mg /L during all of the monitoring events with a maximum concentration of <br />11,200 mg /L. <br />4.1.5 Monitoring Well MW -5 <br />Monitoring well MW -5 is located hydraulically side - gradient of CKD disposal area A2 (Figure 1). <br />Benchmark analyte levels were not determined for well MW -5. Groundwater samples collected from MW -5 <br />are predominantly calcium- sodium - sulfate type waters (Figure 4). The samples exhibit higher dissolved <br />calcium and magnesium concentrations and lower chloride and alkalinity concentrations than other Site <br />wells (Appendix D). MW -5 samples have pH values ranging from 7.3 to 7.7, with no trending of values since <br />well installation. The TDS concentrations are generally lower than those of the other Site wells. The majority <br />of dissolved trace metals concentrations are in the range of or less than the other Site wells. However, <br />dissolved iron concentrations are two to three orders of magnitude greater than the remaining Site wells. <br />A number of constituents have exhibited decreasing concentrations since the first sampling event during <br />the 1st quarter of 2013, these include: dissolved magnesium, sodium, sulfate, and TDS. These trending <br />concentrations indicate that the well was likely not in equilibrium with the surrounding formation and that <br />measured concentrations may not be reflective of native groundwater conditions. <br />4.1.6 Monitoring Well MW -6 <br />Monitoring well MW -6 is located hydraulically downgradient of CKD disposal area A2 as well as <br />monitoring wells MW -1, MW -2 and MW -3 (Figure 1). Benchmark analyte levels were not determined for <br />well MW -6. Groundwater samples collected from MW -6 are predominantly sodium - chloride type waters <br />(Figure 4). The samples exhibit similar major ion concentrations to wells MW -4 and MW -7, and have <br />higher chloride and sodium concentrations compared to those of upgradient Site wells (MW -2 and MW -3). <br />Samples collected from MW -6 have pH values ranging from 8.1 to 8.2, with no trending of values since <br />well installation. The TDS concentrations are generally greater than those of the other Site wells with the <br />�.` Golder <br />010 \81640a\0400\9w har llinstallfieltlrep _(nl- 30apr14 \10381840a gwchanpt _holcim- UOettchar_fnl- 28apr14 vith holcim etlds tlocx <br />Associates <br />