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MRR 02 '95 02.41PM DIVi~RRLS&GEOLOGY <br />DATE: March 2, 1995 <br />TO: Tom Gillis <br />Rece(ved <br />MAR 0 21995 <br />FROM: Tom Schreiner '~:,•~•!~~~?''tiOYiCa <br />RS: Hydrology Review, Final Comments - Incas Mine (110D) <br />Amendment, Permit No. M-86-076 <br />~E~v~a <br />O~'~5~~ , <br />I have completed my review of Bob Hill's response to my adequacy <br />comments of November 18, 1994 as well as follow-up comments by Dr. <br />Harry Posey of the DMG. I offer the comments listed below in <br />addition to Dr. Posey's comments of February 20, 1995. At this <br />stage in the permitting process, it appears that the applicant has <br />not adequately addressed all adequacy questions regarding <br />protection of surface and ground water resouces, has not adequately <br />demonstrated a benign filter cake/waste rock mix, has not provided <br />sufficient baseline hydrologic data, and has not provided an <br />adequate hydrologic monitoring program sufficient to meet the <br />requirements for a designated mining operation. <br />1. The method proposed for disposal of spent ore discusses the use <br />of diversion ditches to manage surface water flows. However, the <br />operator has not provided engineering designs for the ditches or <br />construction techniques to be implemented. Also, the operator <br />discusses the installation of a 5' thick compacted cover. The <br />operator has not characterized the material to be used or provided <br />a permeability to be expected upon compaction. Finally, a <br />vegetative cover on top of the clay cap may be helpful. However, <br />the operator may consider placing 6-8 inches of suitable growth <br />medium (soil) on top of the compacted cap in order to achieve a <br />desirable result. <br />2. Tha operator appears to have resolved concerns for adequate <br />water rights with the State Engineers office. <br />3. The operator proposes fill of filter cake/mine waste into open <br />cuts and shallow depressions while at a moisture content of 25~. <br />The operator further states that the operation will be designed and <br />constructed as a zero discharge facility. Therefore, until the <br />operator has secured an NPDES water discharge permit from the <br />Colorado Department of Health, Water Quality Control Division <br />DGMC/Bob Hill will need to demonstrate that any residual moisture <br />in the Filter cake/mine waste placed as fill will be contained on <br />site and will not discharge toward Little Deadwood Gulch. <br />P.2~z <br />~ncgs. ~/N Z ,~ ~S <br />