2012-06-26_REVISION - C1981019 - Laserfiche WebLink

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Response: Colowyo Coal Company is seeking only to revert back part of the way to the Curve Numbers that were adopted previously based on the NEH recommendations and the Striffler and Rhodes data. By contrast, the increase in Curve Numbers on reclaimed lands in TR -73 seems to have been arbitrary and without technical justification. CCC believes the 76 data points of actual infiltration tests on reclaimed lands, all showing HSG B or higher, and the fact that all nearby mines in the region use Curve Numbers in the 60s which can only be achieved by assuming a soil with infiltration rates as observed in the Striffler and Rhodes study (i.e., HSG B), is sufficient data to justify a revision. If CDRMS cannot reach this conclusion, CCC at least requests the agency delay its action 011 this TR until additional field tests can be performed. • Regarding other changes to Exhibit 7, please explain the rationale behind all substantive changes. In particular, please explain the reasoning for updating the sediment loading parameters in Table 6. Response: The applicable text `Methodologies and Assumptions for Sedimentation Pond Design Evaluations" in Volume 2D was undergoing a revision with the proposed curve numbers, and this section was submitted in its entirety. Table 6 is part of that section. The similarly organized Table 4 in Volume 13 was submitted and revised to keep it consistent with Table 6 Comments presented below relative to Table 6 are also applicable to Table 4. Revisions to Table 6 were included to bring a consistent basis to the sediment delivery estimates for the various sediment ponds. The calculations represented in the final five rows of Table 6 have been prepared pursuant to several different methodologies over the years, although all ultimately trace back to the use of The RUSLE methods. It has become an issue at this time to answer CDRMS recent requests dealing with the inspection protocols for the sediment ponds, in particular the annual inspections which are required to be certified by a professional engineer. By way of the proposed revisions to Table 6, CCC is attempting to make the inspection basis consistent for all of the ponds and to remove ambiguities that may be of concern to an engineer certi the reports. Sediment delivery volume for the older ponds was manually calculated using the sedimentology parameters described in `Methodologies and Assumptions for Sedimentation Pond Design Evaluations" and applying a SDR sediment delivery ratio based on the values presented in the literature. With the adoption of SEDCAD as CDRMS preferred method for determining compliance with the regulation in the design phase, and since the input parameters needed for this calculation in SEDCAD are the same as those historically used for the manual