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C1982-056: TR67 Adequacy 4 August 6, 2009 <br />18. It is the Division's determination that the CRDA underdrain proposed by this revision accomplishes the <br />intent of Rule 4.10.3(5). The presence of the underdrain, as designed, will ensure that the applicable <br />safety factor of 1.5 will continue to be achieved; will serve to increase the stability of the fill by <br />preventing any significant build-up of hydrostatic pressure within the pile; and will protect the surface <br />and groundwater in accordance with the requirements of the Rules. <br />Contour lines (existing), as shown on the Phase I Grading Plan (Sheet No. C-102), reveal the presence of <br />a topographic flow path beginning approximately 500 feet ESE from the coal stockpile tube and running <br />perhaps 800 feet SSE to intercept the Phase I Underdrain. No underdrain has been proposed to occupy <br />this flow path. Please incorporate an additional underdrain at this location, or provide sufficient <br />justification which explains why such an underdrain should not be required. <br />19. The CRDA design proposed has been shown to be stable (with a Factor of Safety >1.5) with respect to <br />any large, circular failure. However, the data provided by NWCC indicate that shallow failures on the <br />face of the fill slope may be somewhat more likely to occur (although not with dire consequences). If, <br />during Phase I or II construction of the CRDA, shallow failures are observed on the face of the fill with <br />any frequency, the proposed slope configuration should be modified (flattened) to prevent such failures <br />from occurring in future phases. <br />Please provide additional language in Section 2.05 of the permit to address actions that will be taken, <br />should there be shallow slope failures observed on the face of the CRDA fill. <br />The Division's proposed decision date is August 24, 2009. Please provide TCC's responses to the Division by <br />August 17, 2009 to allow for the Division's review. Please call me if you have any questions. <br />Sincerely, <br />Janet H. inns <br />Environm tal Protection Specialist II <br />(303) 86 567 ext. 8107 <br />CC: Dan Hernandez, Tom Kaldenbach, Marcia Talvitie, DRMS <br />Attachment: Reclamation Cost Estimate