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*Owl <br />COAL <br />COMPANY aK <br />AEO"tE • PRODUCTION <br />2) DRMS Original Comment: <br />CCC references the 1981 report by Striffler and Rhodes, "Hydrologic <br />and Erosional Characteristics of Regraded Surface Coal Mined Land <br />in Colorado," which includes sample sites at eleven surface mines in <br />Colorado. Specific to Colowyo, the sampling was done on 11 acres of <br />lands reclaimed at Colowyo in 1978. Colowyo now has thousands of <br />acres of reclaimed lands. On page 14 of this report, the authors state, <br />"However, any generalizations about the similarities of surface <br />hydrology or regraded coal mined land from state to state, between <br />areas within a mining region, or even between sites within a mine are <br />risky due to critical site specificity." Thus it is not clear that past <br />studies at Colowyo, let alone studies at other mine sites, provide <br />justification for altering CN values. <br />Colowyo's June 25, 2012 Response to Comment 2 above: <br />CCC is aware of the generalization described on page 14. We further <br />agree based on annual report mapping there was considerably less area <br />of reclaimed spoils in 1981 than exists today, and that acreage was likely <br />in the near the toe of the Streeter Fill reclamation. However, we believe <br />the regional nature of the report is in fact a strength, not a weakness, as <br />discussed below. <br />The justification for changing curve numbers is nevertheless straight- <br />forward and rests on three premises. <br />First, the NEH, which is the recognized document for hydrologic design, <br />clearly states that it is not appropriate to use native soil mapping to assign <br />Hydrologic Soil Group (HSG) values to disturbed lands. Reference is in <br />part 630.0702, which states: <br />"As a result of construction and other disturbances, the soil profile can be <br />altered from its natural state and the listed group assignments generally <br />no longer apply, nor can any supposition based on the natural soil be <br />made that will accurately describe the hydrologic properties of the <br />disturbed soil. In these circumstances, an onsite investigation should be <br />made to determine the hydrologic soil group ". <br />A Western Fuels - Colorado, LLC mining property <br />