2009-08-14_REVISION - C1981019 (3)

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Based on the Division's review of the materials provided on 24 June 2009 and based on the approvals of Technical Revision 73 (curve numbers), Technical Revision 80 (backfilling and grading schedule) and information from CV-2008-004, the Division has the following additional adequacy questions. 4. Please submit general and detailed design information for the temporary sump regarding sizing, spillway placement (Rule 4.05.7) and routing from and to the Prospect Ditch, as required by Rule 2.05.3(4) and Rule 4.05.9. The Division understands the impoundment will be incised (no embankment) and will discharge during both the 10-year and the 25-year storm events. The volume of the sump as represented in the SEDCAD runs provided with the 24 June 2009 responses is 2.44 ac-ft. This volume does not agree with the volume as calculated by the permit text on page Exhibit 7-14R-1 (22' x 335' x 8' = 58950 cubic feet) which is 1.35 ac-ft. 6. Pursuant to Rule 2.05.3(4)(a)(ii), please provide a detailed plan for operation and maintenance of the temporary sump, including dewatering, sediment clean-out, inspections and any necessary repairs following storm events. 7. The Final East Pit Ditch and the Prospect Ditch are included in the background on Figure 1 and Figure 2. This figure does not include the approved North Tributary, East Pit Ditch. Please remove these ditches from Figures 1 and 2 or include all approved post-mining ditches on the figures. It would appear that internal ditch A should be extended to the northeast along the lower boundary of parcel D (19.4 acres) to capture flows as modeled. Please review and correct as necessary. 9. Please specify in the permit how the measures proposed under technical Revision 78 will function in combination with the reclamation schedule approved under technical Revision 80. Please detail the reclamation and timing of each of these temporary ditches and sumps within the TR-80 reclamation schedule. 10. In the responses to TR-78, Colowyo has provided a Prospect Pond model that contains the internal ditches and sumps. This model will obviously change as more of the area is reclaimed and the ditches and sump are reclaimed. This will lead to an out of date Prospect Pond model in Exhibit 7. Please describe how Colowyo will ensure that an accurate and representative model for the Prospect Pond will be maintained in the permit. 11. During the settlement conference phase of Notice of Violation CV-2008-004, there was a good deal of discussion regarding on the ground measures that would need to be implemented and the permitting actions that would need to be submitted to ensure that the Prospect watershed remained stable in the long-term. The first two pieces of that process are the short-term measures (TR-78) and the