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standard should be based on the lower 95 per cent confidence limit of the mean hardness <br />value at the periodic low flow criteria as determined from a regression analysis of site-specific <br />data. Where insufficient site-specific data exists to define the mean hardness value at the <br />periodic low flow criteria, representative regional data shall be used to perform the regression <br />analysis. Where a regression analysis is not possible, a site-specific method should be used, <br />e.g., where hardness data exists without paired flow data, the mean of the hardness during <br />the low flow season established in the permit shall be used. In calculating a hardness value, <br />regression analyses should not be extrapolated past the point that data exist. For <br />determination of standards attainment, where paired metal/hardness data is available, <br />attainment will be determined for individual sampling events. Where paired data is not <br />available, the mean hardness will be used." Given the direction in Regulation 31 and the <br />availability of site specific flow and quality data, it is not clear why SCC is using a value of 400 <br />mg/I. Please explain why SCC bases the parameter limitations on a hardness value of 400 <br />mg/I rather than on site specific data. <br />12. Also on Tables 13 and 15, SCC notes that the detection limit for mercury and sulfide is higher <br />than the receiving stream standard value. Please explain why SCC is not ordering the <br />analysis of these parameters at a detection limit below the standard. <br />13. SCC notes that receiving stream standards were exceeded at surface water monitoring sites in <br />ten instances, detailed in Tables 14 and 16. <br />a. Iron limits were exceeded four times at three Grassy Creek sites. SCC explains that <br />none of the exceedances were at NPDES sites, and three were at upstream sites <br />(SSLGS and SSG1). The Division also observed that, although still above the limit, iron <br />concentrations decreased at the Grassy Creek downstream site (SSG2) on the two <br />occasions that upstream iron concentrations (SSG1) were elevated. Iron limits were <br />also exceeded three times each on the upper and lower Fish Creek sites (SSF11 and <br />SSF12); again iron concentrations were lower at the downstream site than at the <br />upstream site in each instance. <br />b. Table 16 indicates that sulfide limits were exceeded three times at NPDES3, with <br />values ranging from .0024 to .007 mg/I. The water quality data sheets in Appendix D <br />for NPDES3 indicate values ranging from .03 to .05. Other sheets in Appendix D <br />indicate that the detection limit for sulfide is .2. Please explain these discrepancies. <br />14. Seven of the ten monitored spoil springs show a decreasing EC trend, two are stable, and one, <br />Spoil Spring 9, shows an increasing electrical conductivity (EC) trend. The decreasing trend in <br />the seven springs began, on average, eleven years after backfilling and grading. Spoil Spring 9, <br />upstream of Pond 008, is downgradient of the last Wadge pits backfilled in 1999 and 2000. <br />Page 4 of 5