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Division. Chemical control is the only method used at the Seneca II operation, there has <br />been no biological or mechanical controls used. <br />48. Please revise the calculation of ground water flow velocity on page 2.04-52 using a <br />value for porosity that is significantly less than 14% (we suggest a value of 10%), <br />and revise associated analyses or references in the permit application. Although <br />Robson and Stewart reported 14% as an average and used it in their numerical <br />simulation, it represents total porosity, rather than the effective porosity value that is <br />required in a calculation of Darcy seepage velocity. SCCC's bulk density logs show <br />that total porosity of the beds in the underburden (the only interval logged) that are <br />most likely to be permeable (sandstone) are around 15%, but the low hydraulic <br />conductivity values shown for the lower member of the Williams Fork in Table <br />2.04.7-T2 indicate effective porosity would be significantly less than the total <br />porosity shown on the logs. Based on Williams and Clark's (1992) study, it is <br />probable that clay minerals reduce effective porosity to a value that is significantly <br />less than total porosity. Their mineralogic analysis (Table 15) found that core <br />samples from the lower member of the Williams Fork contained abundant clay <br />minerals (mainly kaolinite). Their comparison of hydraulic conductivity and <br />permeability to air (page 23 of their report) concluded that permeability was reduced <br />to less than the theoretical maximum probably as a result of clay minerals plugging <br />the sandstone pores. Although Williams and Clark's data may suggest effective <br />porosity would be only a fraction of the value of total porosity, they analyzed <br />permeameter samples which would not have had fracture porosity; therefore, an <br />effective porosity value of 10% is suggested relative to total porosity of 14% or 15%, <br />rather than some smaller effective porosity value. <br />Response: The text beginning on or about page 2.04-51 in Section 2.04.7, Hydrology <br />Discussion has been changed to revise the calculation to use an effective porosity of 10 <br />percent. Revised materials are included in this PAP response package. <br />49. Please revise the calculation of mine water discharge to alluvium at the top of page <br />2.05-85 so that it uses the 2.5 ft/day hydraulic conductivity value noted above in our <br />Comment 14. <br />Response: As a result of the discussion of this comment in a conference call with <br />CDRMS on February 24, 2010, it was agreed that this change would not occur based on <br />the following. A horizontal-flow conceptual model as described in Comment 14 and <br />requested by this comment is not applicable in this case. Groundwater flow from the <br />mine workings to the alluvium could only be upward, normal to the bedding plane of the <br />bedrock, and that the vertical hydraulic conductivity would thus be applicable. <br />50. Please revise the mine inflow and drawdown calculations in Section 2.05.6(3)(b)(iii) <br />as follows: <br />a) Extend the time period to include the end of the first 60-month permit term and 30 <br />years after the end of the 60-month permit term.