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April 2014 11 10381640A <br />downgradient wells MW -2 and MW -3 and side - gradient well MW -5, but lower TDS concentrations than <br />downgradient wells MW -4, MW -6, and MW -7. <br />The majority of dissolved trace metals concentrations in samples collected from MW -1 are in the range of <br />or less than the other Site wells, however, dissolved selenium concentrations are two to three orders of <br />magnitude greater than the other Site wells. <br />4.1.2 Monitoring Well MW -2 <br />Monitoring well MW -2 is located hydraulically downgradient of CKD disposal area A2 (Figure 1). <br />Groundwater samples collected from MW -2 are predominantly sodium - chloride type waters (Figure 4). <br />The samples exhibited similar major ion concentrations as well MW -3, and have higher alkalinity and <br />lower dissolved calcium, magnesium and sulfate concentrations than most Site wells (Appendix D). The <br />MW -2 samples have pH values ranging from 7.9 to 8.4, and remain consistent with values observed prior <br />to CKD material placement in disposal area A2. <br />The majority of dissolved trace metal concentrations in samples collected from MW -2 are in the range of <br />those observed in the other Site wells. From September 2010 to present, only three of the 16 constituents <br />have exceeded established benchmark concentrations, including: <br />IN Barium - During the September 2010 monitoring event, the concentration of barium was <br />2.09 mg /L, which slightly exceeded the established benchmark concentration of 2.0 mg /L. <br />The remaining 12 samples collected from MW -2 since 2010 have not demonstrated <br />concentrations of barium in exceedance of the established benchmark concentration. <br />• Boron - During the August 2011, November 2011, and May 2013 monitoring events <br />boron was detected at concentrations of 0.78 mg /L, 0.79 mg /L, and 0.76 mg /L <br />respectively. These concentrations slightly exceeded the boron benchmark concentration <br />of 0.75 mg /L. The remaining 10 samples collected from MW -2 since 2010 have not <br />demonstrated concentrations of boron in exceedance of the established benchmark <br />concentration. Since detections ranged from 0.67 mg /L to 0.74 mg /L during the 1999 and <br />2000 sampling events, the boron benchmark level for MW -2 was set at the regulatory <br />standard of 0.75 mg /L. Although there have been some values greater than the <br />benchmark level the 0.64 mg /L to 0.79 mg /L range of values observed since 2010, is <br />similar to the 1999 to 2000 range of values. <br />• Iron - Since 2010, the concentration of iron exceeded the established benchmark of <br />0.71 mg /L during five sampling events, with a maximum concentration of 1.1 mg /L. The <br />remaining 8 samples collected from MW -2 since 2010 have not demonstrated <br />concentrations of iron in exceedance of the established benchmark concentration. <br />4.1.3 Monitoring Well MW -3 <br />Monitoring well MW -3 is located hydraulically downgradient of CKD disposal area A2 (Figure 1). <br />Groundwater samples collected from MW -3 are predominantly sodium - chloride- bicarbonate type waters <br />(Figure 4). The samples exhibit similar major ion concentrations to well MW -2, and have the highest <br />Golder <br />is \10 \81640a\ 0400\ gwcharwellinstallfieltlrep _fnl- 30apr14H 0381840a gwchartpt _holism- boettcher_(nl- 28apr14 with holism etlits.tlocx 9 Associates <br />