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standards and spiked additions of 75%to 125%(or sometimes 80%to 120%)of the actual <br /> value. This translates to an intrinsic analytical error of ±25% in reported sample <br /> concentrations, whereby error propagation is reduced, but not eliminated, by repetitive <br /> sampling (e.g. over the course of several quarters and analytical duplicates). Therefore, a <br /> COC concentration 0.006 mg/L above a groundwater standard of 0.03 mg/L (i.e. within <br /> 20% of the standard) for one sampling event may or may not represent the actual <br /> concentration of the COC in groundwater, or an exceedance. However, if similar <br /> exceedances occur over multiple sampling events, this indicates that the concentration <br /> trend may be valid. Eight quarters of groundwater sampling for MW-06 and MW-10 has <br /> confirmed elevated uranium concentrations for these monitoring wells. However, given <br /> the range of acceptable analytical error in laboratory QA reporting of±25%, the average <br /> uranium concentrations of 0.036 and 0.033 mg/L for MW-06 and MW-10 over the eight <br /> quarters of sampling are well within this range of error, and regulatory exceedance of the <br /> Regulation 41 Standard cannot be confirmed. <br /> Looking closely at non-COC concentrations for the Site (i.e. selenium, iron, nitrate, and <br /> manganese),trends begin to emerge. Iron concentrations have decreased(Figure 11) in all <br /> wells that shortly after monitoring wells were installed,which indicates that the likelihood <br /> of future iron exceedance is unlikely. Nitrate concentrations have not exceeded Regulation <br /> 41 Standards and appear to fluctuate seasonally (Figure 11), associated with summer <br /> fertilization of upgradient fields adjacent to the Knox property. Manganese exceeded <br /> standards one time in P-4 and was 10 times the concentration of the previous quarter. This <br /> was likely an outlier as no other monitoring wells(adjacent or far away from P-4)exceeded <br /> the Manganese standard. <br /> Selenium concentrations have remained well below the Regulation 41 Table 1 Standards <br /> for all wells, except MW-06 and MW-10. Selenium concentrations in these wells have <br /> decreased steadily (Figure 12) since monitoring well installation and will not likely <br /> increase, without a major change in redox state (i.e. oxidation potential increases <br /> substantially) that transitions Se(4+) to Se(6+), thereby increasing Se solubility (Table 8 <br /> and Appendix D). Based on the current state of oxidation (relatively high), increased <br /> Loveland Ready-Mix Concrete I 1 December 2019 <br /> ,0,0�,_ spi baselmoNatcrqualinsumman doo T E L E S T O <br />