2010-11-09_REVISION - C1981019 (2)

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6. Based on the backfilling and grading schedule (Map 29), Colowyo will be constructing portions of their permanent, post-mining drainage channels over several reclamation seasons. In order to ensure that the yearly channel construction has been completed as designed, the Division has requested that Colowyo provide a yearly as-built certification of all ditch segments constructed during a reclamation season. The Division has requested that this information be included in the Annual Reclamation Report. Please revise the text in Permit Section 4.05.4 and in the introductory text to Exhibit 7, Item 14 committing to providing the Division with yearly as-built certifications for all post-mining drainage channels constructed in a reclamation season in the Annual Reclamation Report for that year's reclamation. The as-built certification will, at a minimum, detail the construction of each channel segment (Width, depth, riprap D50, etc.) and, provide a map or drawing of each channel segment, reference the exhibit that was used to determine design requirements for the channel segment and provide representative pictures of each channel segment constructed. Response: Colowyo has revised the text in Sec 4.05.4 detailing Colowyo's commitment to providing the Division with yearly as-built certifications for all post-mining drainage channels constructed in a reclamation season in the ARR for that year's reclamation. The requested text has also been added to the Introductory text of Exhibit 7, Item 14. Rule 4.05.9 - Impoundments Colowyo has provided revised page Exh.7-14R-1, which describes the five proposed stock tanks in the Prospect watershed area of the East Pit. The text in the third paragraph of revised page Exh.7-14-R1 does not accurately describe the proposed stock tanks either by name and/or by year of construction when compared to Map 12 and the figures contained in the SEDCAD modeling. This deficiency was identified and discussed during both the 18 August 2010 meeting at the Mine and the 13 October 2010 meeting at the Division's office. Please review the stock tank information provided on revised page Exh.7-14R- 1, Map 12 and the SEDCAD modeling and correct this information as necessary. Response: Revised materials are provided to address this issue. 8. Colowyo has provided revised page Exh.7-14R-2, which describes the Prospect watershed condition in three future years, with the 2017 condition identified as the worst case hydrologic condition. Please demonstrate, through SEDCAD modeling, that the Prospect Pond spillway system complies with Rule 4.05.9(2)(c)(ii) for the 25-year 24-hour storm event for the 2017 watershed condition. Response: Colowyo has provided the requested additional SEDCAD model that analyzes the 25 year event. 9. Colowyo has provided new, proposed generalized stock tank design as Figure 2.05-6. This stock tank design will be used to construct the five stock tanks proposed in the Prospect Watershed of the East Pit. Colowyo also has an approved stock tank design in Exhibit 7, Item 11, which was used to construct all of the stock tanks that are currently on the ground in the East Pit and Section 16 Pit reclamation. Colowyo will need to retain the stock tank design in Exhibit 7, Item 11 as it is still valid for the existing stock tanks. The Division recommends that Colowyo include Figure 2.05-6 in Exhibit 7, Item 11 as well, so all stock tank designs are in the same location. The Division also requests that Colowyo provide a cover page for Figure 2.05-6 as well as a short description stating which stock tanks this design will be used to construct. Finally, as discussed in the 13 October 2010 meeting, Colowyo needs to update Figure 2.05-6 to accurately represent the stock tanks as they will be constructed in the prospect watershed, including the routing of the runoff for stock tanks not constructed directly in the post-mining drainage channels. Response: Colowyo believes the appropriate place for the new design is within Section 2.05 as proposed. Exhibit 7, Item 11 is only intended to represent the historic design elements for Colowyo Coal Company, L.P. • 5731 State Highway 13 • Meeker, CO 81641 T + 1 970 824 1578 • F +1 970 824 1598 • http://prospect.riotinto.org/irj/portal