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CMC—Henderson Operations <br /> 5-Quarter Water Quality Data and Baseline Parameters Report <br /> May 2014 <br /> 1 Table 3-3: MLGW-17 Numeric Protection Limits <br /> Iron,dissolved 5 Table 3,CBSG <br /> Manganese,dissolved 0.79 Ambient <br /> ' Selenium,dissolved 0.02 Table 3,CBSG <br /> Zinc,dissolved 2 Table 3,CBSG <br /> Conductivity,umhos/cm NA(report) NA <br /> ' pH,s.u. 5.9—8.5 Ambient <br /> Sulfate,mg/L NA(report) NA <br /> ' Notes: <br /> Table 3,CBSG:Agricultural Use Standards <br /> Ambient:Dissolved manganese—refer to Establishing Background Threshold Values(BTV)for Manganese <br /> 1 (Gateway Enterprises,2012);pH-see Appendix C <br /> 3.4 Establishment of Ambient pH NPLs at Mill POCs <br /> Henderson recently completed and submitted to the DRMS the results of a Groundwater Quality <br /> Assessment for MLGW-7 (AJAX and Clear Creek Associates, 2014b)in response to measured pH values <br /> that fell below the established NPL range of 6.5 —8.5. The report concluded that the pH measurements at <br /> MLGW-7 and other locations do not appear to be indicative of seepage impacts and are more likely <br /> attributable to natural fluctuations. It was recommended that Henderson work to establish pH NPLs at <br /> MLGW-7 and other POC wells that appropriately bracket naturally occurring conditions. Consistent with <br /> this recommendation, Henderson has developed and is proposing a NPL range for pH of 5.9 — 8.5 <br /> ' standard units at all Mill POC locations using ambient data consistent with established methodologies for <br /> developing background threshold values (BTVs). This assessment is presented in Appendix C - <br /> Establishing Background Threshold Values(BTV)-Henderson Mill(Gateway Enterprises,2014). <br /> 4.0 Monitoring Frequencies <br /> Consistent with monitoring frequencies summarized in GWMP Table 6-2,POC wells will be monitored <br /> at the frequency summarized in Table 4-1: <br /> Table 4-1: Monitoring Frequency <br /> MLGW-15 3x/ ear* Groundwater <br /> MLGW-ACR 3x/ ear* Groundwater <br /> MLGW-17 3x/ ear* Groundwater <br /> Notes: <br /> *3x/year—samples shall be collected during spring run-off(Apr-May),summer months(July-Aug)and low flow(Sep-Dec). <br /> ' Page 7 of 9 <br />