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;COAL COMPANY 4 TY. PEOPLE PRODUCTIO14* seeks to revert toward the historically used Curve Numbers for all other areas. This change would bring the Colowyo modeling more into line with the neighboring mines in Moffat and Routt Counties as well as the recommended practices presented in Part 630 "Hydrology" of USDA NRCS National Engineering Handbook (NEH). CCC does not believe that more accurate modeling results from simply increasing the Curve Numbers without any technical or site specific basis, although doing so clearly produces more conservative modeling (i.e., larger runoff). The root of the issue is the selection of Hydrologic Soil Group (HSG) for the reclaimed lands. This affects the selection of Curve Number in the various USDA /NRCS published tables that relate curve numbers to specific land use and surface condition for a specified HSG. Selection of the runoff curve number (CN) in turn directly affects the magnitude of runoff for any modeled storm event. Colowyo Coal Company identified the soils on the mine site as HSG C only as a condition of approval of TR -73. Colowyo Coal Company's professional engineering hydrology consultants do not believe that reclaimed soils should be assigned a HSG C in this case. In the review process of TR -73, in the May 11, 2009 response to the agency's second round comments, CCC explained the basis of the assignment of HSG B to reclaimed areas, elaborating on the concept that wholesale removal and replacement of existing soils destroys all shallow soil structure, and would be expected to result in a higher infiltration rate than the native undisturbed soil. This approach is consistent with the recommendations for "Disturbed soils " presented on page 7 -5 of Part 630 of the NEH, and is also strongly supported by the results of the OSM sponsored 1981 Striffler and Rhodes study. The technical arguments presented in the TR- 73 review process and the results of the 1981 infiltration study were also the basis for the selection of HSG "B" soil for reclaimed lands in Exhibit 7 Hydrology Methodology and Assumptions as submitted with TR -56 in 2003. The previous hydrologic consultants (Western Water Consultants) and the current consultant (Environmental Solutions, Inc.) believe the approach is sound and is in accordance with accepted engineering practice as indicated by their engineering certifications on the several submittals. In the end however, CCC was unable to persuade CDRMS staff that this approach is correct and agreed to delete from Table I the column that had A Western Fuels - Colorado, LLC mining property