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6) Well Installation in Waste Rock Pile: <br />Cotter's proposed plan for installation of a well in the waste rock pile appears adequate, <br />but should be done with independent oversight from a knowledgeable and trained <br />hydrogeologist /geologist, and experienced personnel to ensure the well is installed correctly. <br />7) Installation of Lysimeters in Waste Rock Pile: <br />Cotter's plan to install pan lysimeters in the waste rock pile appears adequate, but <br />should be overseen by a knowledgeable and trained hydrogeologist with pan lysimeter <br />experience. Pan lysimeters are easy to install improperly and are below ground so it is difficult <br />to ascertain whether they were correctly installed. Supervision by an independent trained <br />hydrogeologist will provide additional assurance that the data from the pan lysimeters is <br />reliable and accurate. <br />Denver Water would like the opportunity to discuss these comments with your office as <br />it currently does not support approval of the September 21, 2012 Dewatering Plan in its current <br />form. At a minimum, comments 1 through 7 should be addressed above, and to achieve a <br />greater likelihood of success, Cotter should be required to jointly move forward with in -situ <br />treatment and mine pool dewatering, rather than be allowed to pursue a decoupled approach. <br />CC: John S. Hamrick <br />Canon City Mill <br />P.O. Box 1750 <br />Canon City, Colorado 81215 -1750 <br />Sincerely, <br />/ 6=e P` <br />Tom Mountfort <br />Denver Water <br />Environmental Compliance Supervisor <br />Page 4 of 4 <br />Denver Water Comments Re: Cotter Dewatering Plan (Permit No. M- 1977 -300) <br />