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Comment Response COMMENT RESPONSE SUBMITTAL Rule 2.05.3(41 Ponds, impoundments, and other treatment facilities and diversions Page 1 40. The PR-02 submittal does not include detailed design plans for four proposed sediment ponds. As required by Rule 2.05.3(4), please provide general and detailed design plans for each sediment pond, including the discharge structures. In particular, parts (ii) and (iii) require plans be submitted to the State Engineer and/or MSHA and be included as part of the permit application as well. Applicable portions of Rules 4.05.6 and 4.05.9 should also be considered, including necessary stability analysis and geotechnical investigations for each structure. Response: Amore detailed plan based on recent survey data is included for each of the proposed impoundments. This information is being incorporated into the Sediment Control Plan and associated SEDCAD runs provided in Exhibit 7, Item 20. For the three impoundments proposed under this plan, the structures have been specifically designed to not require MSHA review. Additionally, it has been determined through discussions with Colorado State Engineer Office staff that these three impoundments do not require permitting through that office. Exhibit 7, Item 15 (Volume 2C) of the current permit contains a stability evaluation for the eight existing sediment ponds that existed at the time CTL/Thompson performed the stability analysis in 1998. In that analysis, the ponds were broken into two groups. One group contained the larger embankments with typical embankment heights up to 22 feet, while the second set included embankments less than 11 feet in height. Both groups were analyzed and produced a factor of safety of 2.0 or greater, well in excess of the regulatory limit of 1.3 required under 4.03.1 3) e (ix). Exhibit 7, Item 20 Part F provides a similar report containing a 2003 geotechnical evaluation for two of the three impoundments associated with the South Taylor mine plan (Section 28 Pond and Section 21 Pond). The introductory text to Exhibit 21, Item 1 discusses the geotechnical evaluation for the third (West Taylor) impoundment. All three of the proposed sediment ponds associated with the South Taylor project have embankments with upstream slopes of 2H:1V and downstream side slopes of 3H:1V, which is similar to previous analysis assumptions. Total embankment heights for the new ponds are similar to the 22 feet assumed in the prior analysis, the depth of impounded water is similar, and the embankment crests are wider. Thus, it can be concluded that the factor of safety for the four new impoundments is greater than 2.0. Again, this is well below the regulatory requirement. 41. The applicant provided SEDCAD4 modeling results dated August 4, 2006 for four ponds proposed for the South Taylor mining proposal. These materials are part of Exhibit 7, Item 20 of the PR-02 application rna[erials. Introductory text is included that describes the methodologies and assumptions for sedimentation pond design and evaluations. In Section 1.4, Hydrograph Response it is stated that "medium and fast hydrograph responses were identified as representative for mine areas" yet fast and slow hydrograph responses were used exclusively in the SEDCAD design runs. Please explain. Response: The previous SEDCAD runs has been substantially revised. In general, all of the disturbed areas use the Fast or medium response. Inputs for each run are available in the "Subwatershed Hydrology Detail" section of the various SEDCAD reports under the "UHS" heading.