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As an extreme example of this, assume a 1,000 acre hypothetical watershed that is 50% <br />undisturbed land (CN=57 based on good condition rangeland) and 50% disturbed with topsoil <br />stripped (CN=85). Using area weighting of the two curve numbers results in an overall curve <br />number of 71. In SEDCAD, that 1,000 acre watershed with a curve number of 71 produces <br />15.86 acre-feet of runoff. The same watershed modeled using two independent curve <br />numbers produces 27.58 acre-feet of runoff, nearly twice as much. Thus, weight -averaging <br />always tends to under estimate runoff flows because the higher curve numbers produce <br />disproportionate responses. <br />No changes have been made as a result of this comment <br />t. Please explain why the channel near the 8000 -foot elevation in Exhibit 7, Item 20, Part <br />G is not the representative channel; it has a much larger total drainage area than the <br />channel at the 7900 -foot elevation (although the fill area is smaller). <br />Response: As noted previously, the footprint of the East Taylor Excess Spoil boundary has <br />changed with this submittal. This has resulted in changes to the terrace ditches shown on Map <br />41 and 41A. Regardless, we agree with the comment and the 8000 foot ditch is more <br />representative. We have revised the text and SEDCAD model accordingly. <br />Exhibit 7, Item 20, Part G is resubmitted with this submittal. <br />19. Map 41A shows that the Taylor Tributary Ditch appears to run through the fill and over the face <br />of the West Taylor Fill. Pursuant to Rule 4.09.2(7), all"... surface water runoff from the runoff area <br />above the fill shall be diverted away from the fill ... ". Please review the location of the Taylor <br />Tributary Ditch and revise its location as necessary to comply with Rule 4.09.2(7). <br />Response: This comment was discussed in detail during a meeting at the mine with Jim Stark <br />of the DRMS staff on June 9, 2015. First, note that the question refers to the West Taylor Fill <br />but should have discussed the East Taylor Fill limits. More generally, the limits of the Excess <br />Spoil (Permanent Fill) boundaries have changed on both Map 41141A and Map 45 as a result <br />of this meeting and a clearer understanding of the regulatory definitions of Excess Spoil and <br />Valley Fills. <br />In both cases, the footprints of the Excess Spoils have been reduced. The result of this <br />change is that the location of the Taylor Tributary Ditch does not cross the fill relative to the <br />requirements of Rule 4.09.2 (7). Also as a result of these changes, the number and location or <br />the terrace ditches have been changed on Maps 41 and 41A. <br />Maps 41, 41A, and Map 45 are resubmitted as a result of this comment. <br />20. Map 41S shows that the West Taylor East Tributary Ditch begins in the reclaimed South Taylor <br />Pit at approximately station 76+00. The start of this ditch allows for approximately 2,000 feet of <br />uncontained sheet flow over the reclamation prior to entering the ditch. Please review the <br />starting point for the West Taylor East Tributary Ditch in the South Taylor Pit and <br />consider extending this ditch to the capture the uncontained sheet flow. <br />Page 11 <br />