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ARCJaD I S ,,.sign&Consottanby <br /> MEMO builta assetural s and <br /> built assets <br /> Arcadis U.S.,Inc. <br /> To: Copies: <br /> 600 S.Cherry Street <br /> Daniel J. Arnold, Esq. Jason Kerstiens, Jeff Gillow, Jeff Suite 600 <br /> Jackson Denver <br /> Colorado 80246 <br /> Tel 303 316 6500 <br /> From: Fax 303 316 6599 <br /> Tim J. Cox, PG, CGWP <br /> Date: <br /> June 7, 2016 <br /> Subject: <br /> Arcadis Review of Cotter Technical Revision 23 <br /> Arcadis U.S. Inc., reviewed Cotter's Technical Revision 23 (TR-23)for the Schwartzwalder Mine, located <br /> near Golden, Colorado. TR-23 proposes to excavate residual waste rock within the alluvium along <br /> Ralston Creek and place the waste rock on either the existing North or South waste piles, or on both. <br /> Three alternatives were evaluated for disposal of the additional waste rock -at the existing waste piles, in <br /> the glory hole, and off site. Cotter's decision to place the waste rock on the waste piles was based on <br /> avoidance of potential safety and environmental hazards with the other two alternatives, and lower cost of <br /> the on-site disposal. The mine permit has approximately 205,000 cubic yards (cy) of unused yet permitted <br /> capacity at the waste piles, and the volume of additional waste rock is estimated to range from 32,000 to <br /> 54,000 cy. The additional waste rock will eventually be covered and vegetated to the same standards as <br /> the existing waste piles. It is Cotter's belief that removal of this residual waste rock will eliminate a <br /> contaminant source at the mine. <br /> Removal of the residual waste rock along the alluvial floodplain may result in some level of water-quality <br /> improvement in Ralston Creek. Disposal of the waste rock at an off-site location would be the preferred <br /> alternative because that would remove the contaminated material from the Ralston Creek watershed. But, <br /> considering that permitted waste piles with excess capacity already exist, on-site placement of the waste <br /> rock on the waste piles is a reasonable disposal option. The additional waste rock would be placed on top <br /> of the existing waste piles, which would keep the material at a higher elevation than the existing piles and <br /> even further out of the floodplain. If properly covered, this should minimize the potential of waste rock <br /> leachate to impact the water quality of Ralston Creek. <br /> Page: <br /> 1/2 <br />