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January 30, 2013 <br />To: Brock Bowles <br />From: Susan Burgmaier <br />Re: Elk Creek Mine (Permit No. C- 1981 -022) <br />2010 and 2011 Annual Hydrology Reports <br />Adequacy Review <br />Per your request, I looked over your Elk Creek 2010 AHR comments (primarily Item 4 of <br />your November 18, 2011 letter) and the response from Oxbow Mining, Incorporated <br />(OMI). I also looked at the 2011 AHR to determine whether your identified concerns are <br />still problematic. My findings on your comments on Item 4 of the 2010 AHR issues are: <br />4. In general, most of the elevated constituents you identified remain a concern. <br />OMI mentioned, in their response, that they changed labs in 2010. The issues <br />you identified could well have been a result of the lab change. Ideally, duplicate <br />samples would have been sent to the new lab and the old lab for comparison. In <br />the absence of that we will have to look at future data and see if any trends <br />develop. If they do, then we will need to try to determine whether these trends <br />are mine related impacts or lab change related. <br />a. Site NF -3: Zn, CN, Chromium -VI, NO3 /NO2. and Se have all decreased, <br />but remain elevated over historic data; B remains elevated with no <br />decrease. Chromium -III and Cl have decreased back to historic values. <br />b. Site NF -1: Chromium -VI, CN, Se, and Zn have all decreased, but remain <br />elevated; B remains elevated with no decrease. Chromium -III and Ag <br />have decreased back to historic values. You mentioned an increase in <br />Chlorine — I didn't see that in the data. Chloride had been elevated but is <br />back to the historic range. <br />C. Well BC -1: As, NO3 /NO2. and Zn have decreased, but remain elevated. <br />d. Well EC -14: As, Fe (dissolved) and Zn remain elevated. NO3 /NO2 has <br />decreased close to the historic range. <br />e. Well EC -15: As, PO4, Zn have decreased but remain elevated over <br />historic data. Fe remains elevated. NO3 /NO2 has decreased to within the <br />historic range. Cl decreased to a value below the historic range. <br />f. Well SC -1: As has decreased but remains slightly elevated. NO3 /NO2 has <br />decreased to within the historic range. <br />g. Well SC -3: As is back within the historic range. <br />