2013-04-26_REVISION - C1981019 (2)

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COAL COMPANY AEOPLE • PRODVICTIO14 channels and the functioning of ponds. The effectiveness of these structures will determine if Colowyo is in compliance with the Division's permit and with your CDPS permit and will be important in the context of future bond release applications. We encourage Colowyo to consider these factors when proposing modeling updates, when constructing structures, and when scheduling reclamation. Colowyo's Response: Colowyo believes that the Division's expectations of conditions under which these structures, the approved designs, and the modeling inputs are reasonably expected to physically, and by modeling assumption, maintain stability and proper function, need to be clearly defined so that additional discussion and evaluation of the applicable regulatory mandates can be applied in this case. Division Comment (Fourth Adequacy) No further response is required of Colowyo. However, based on the following history of incidents at Colowyo, the Division believes that it is not unreasonable to use the existing curve numbers for the hydrologic models: • Overtopping of Prospect Pond. This is relevant because model inputs between the East Pit areas and other portions of the mine, such as the West Pit area, are similar. Colow oy s Response (Fourth Adequacy): Colowyo continues to maintain the firm stance that the August 9, 2008 storm event was exceptional, and the intensity of that event, not a deficiency in design, construction or maintenance of the structures impacted caused the overtopping of Prospect Pond. To our knowledge, this is the only example of a pond being overtopped at Colowyo, under "storm conditions. • The need to rebuild East Taylor Ditch in 2012. Colowyo'sResponse (Fourth Adequacy): Colowyo believes it is not uncommon for maintenance of these structures to be necessary during the first year or two post- construction until vegetation communities become well established in the areas reporting to the ditches. Colowyo does not have a systemic history of requiring substantial maintenance of these structures post - construction, but occasionally it is necessary. Colowyo also has an approved Rill and Gully Plan (Section 4.14.6 of the PAP) to identify these areas in the spring and maintain erosion accordingly. The plan was added s eci icall to promptly identify and mitigate issues such as the East Taylor Ditch erosion that can occur more frequently in newly regraded and topsoiled areas. As shown in older reclamation units, erosion subsides in each unit as each area ages A mining property of Western Fuels- Colorado, A Limited Liability Company