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Page 2 of 2 <br />risky due to critical site specificity. " Thus it is not clear that past studies at Colowyo, let alone studies at <br />other mine sites, provide justification for altering CN values. <br />Again, the Division stands by our assertion that infonnation from other mines and information from a <br />small area on Colowyo Mine is not enough information to identify all reclaimed land on Colowyo as C <br />soils. As CCC states in the response letter, per NEH, an onsite investigation of disturbed lands should be <br />made to determine HSG. <br />Additional information would provide better rationale for altering the CNvalues. This could include site <br />speck infiltration tests and /or calibration of existing models using rainfall and runoff data. <br />Based on the response letter, it appears that CCC is willing to consider the idea of performing on -site <br />infiltration tests. The Division believes that this is the best course of action to detennine soil types of <br />disturbed areas. It would be best to perform these in any areas where revised modeling is planned. To <br />help facilitate the process by insuring that CCC and the Division are in agreement on methodology, the <br />Division would like to review the plan for any infiltration tests prior to implementation. <br />For any revised modeling in new mining areas (e.g., Collom), the best course of action is to use the best <br />available information to characterize future disturbed soils. Data from extensive infiltration tests at the <br />existing mine site would be appropriate to use in determining HSG values at Collom because this would <br />become the best available information. <br />Regarding other changes to Exhibit 7, please explain the rationale behind all substantive changes. In <br />particular, please explain the reasoning for updating the sediment loading parameters in Table 6 <br />No additional comments. <br />In accordance with Section 34 -33- 116(5) of the Act, a proposed decision approving or denying this <br />application is due on July 3, 2012. If not already done, please request an extension of this deadline. <br />If you have any questions, please contact me. <br />Sincerely, <br />Robert D. Zuber, P.E. <br />Environmental Protection Specialist <br />cc: Tom Peterson, Environmental Solutions, Inc., P.O. Box 2996, Cheyenne, WY 82003 <br />