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Page 2 of 2 <br />this? It has been the Division's belief in the past that the models have underestimated flows. This was <br />part of the impetus for TR -73. <br />It is still the Division's belief that additional infiltration data collected at Colowyo (beyond the limited <br />data from the 1981 Striffler and Rhodes study) would lead to a more accurate characterization of the soils <br />of reclaimed lands. However, in the December 13, 2012 letter, Colowyo makes compelling points related <br />to how the mining process increases permeability of the underlying soil, and how the practices of ripping <br />the soil and roughening topsoil will indeed increase infiltration. In future reclamation efforts, it is <br />essential that Colowyo continue these practices. <br />Also, the Division does recognize that the data from Striffler and Rhodes, while somewhat limited, points <br />to reclaimed lands having A or B soils at part of the Colowyo site as well as at other sites in Colorado. <br />COMMENT #3 <br />The condition of Colowyo's mine site will change drastically as reclamation progresses, and compliance <br />with water quality regulations in the past is not an assurance that future conditions at the site will also <br />result in compliance. Therefore, one cannot say that past compliance is justification for lowering curve <br />numbers. <br />The Division is still considering whether or not additional infiltration testing is necessary to justify the <br />proposed curve number changes. After the questions in this letter are answered by Colowyo, we will <br />make this decision. <br />COMMENT #4 <br />My apologies for not being more clear when I repeated the original comment in my July 2, 2012 letter. <br />What I meant to say is that, in the Division's opinion, Colowyo did not answer the question. Please <br />describe how each of the values in the sediment loading section of Table 6 is calculated, including the <br />sources of information. This should be done in a very direct manner, possibly using an example. This <br />issue has also been briefly discussed with Colowyo staff (Kurt Blunt) at the mine's administration office. <br />GENERAL COMMENT <br />It is very important to consider what is happening on the ground. The SEDCAD models are valuable <br />information, but the Division is also concerned about the stability of channels and the functioning of <br />ponds. The effectiveness of these structures will determine if Colowyo is in compliance with the <br />Division's permit and with your CDPS permit and will be important in the context of future bond release <br />applications. We encourage Colowyo to consider these factors when proposing modeling updates, when <br />constructing structures, and when scheduling reclamation. <br />Please contact me (extension 8113) if you have any questions. <br />Sincerely, <br />� Z /, <br />Robert Zuber, P.E. <br />Environmental Protection Specialist <br />