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Response 10 DRMS Comments <br />Enuironmen181Protection P/an, <br />Denison Van 4Mine <br />Response to Technical Adequacy Comments <br />Van 4 Mine Environmental Protection Plan <br />This document provides response to technical adequacy comments received from the <br />Colorado Division of Reclamation and Mine Safety (DRMS) on the Environmental <br />Protection Plan (EPP) for the Denison USA Corp. (Denison) Van 4 Mine (Permit M-1977- <br />032), dated December 2010. This mine is located in Montrose County. Comments <br />provided by DRMS have been reproduced and presented in italic print. CDM's <br />responses are provided in standard font. <br />Comments provided by Mr. Bob Oswald, DRMS, dated <br />February 18, 2010 <br />General Comments <br />Comment 1 OrePadLiner. As shown by UNSAT-H modeling, the potential for percolation <br />of water to groundwater resources from the waste rock and ore stockpiles does <br />exist though the model indicates that it may be minimal. As such, the <br />requirement for lined ore pads is justified. <br />Response Acknowledged. <br />Comment 2 Ore Pad Size. The site maps depict acceptable liner locations. All are shown to <br />be 100 ft x 100 ft, a standard size which comports with the written description. <br />Response During the ore pad design for the mine, existing surface features, <br />required operations, and ore production rates were evaluated to locate <br />and size the ore pad. The ore pad design (see Attachment K - Ore <br />Storage Pad Drawings and Specifications) provides information on the <br />ore pad location and dimensions. In addition, EPP replacement pages and <br />a figure are provided to consistently present the ore pad location and <br />dimensions. <br />Comment 3 Ore Pad Oeotextile?lalerial. The Division and Denison agree that due to the <br />inherent limitations of the onsite soil for use as a soil liner, an impermeable geo- <br />membrane is required. Denison has proposed using a 30-mil PVC liner, but the <br />Division recommends that PVC not be used, since there is evidence that it can <br />degrade fairly fast, even when covered. The Division suggests that an LLDPE <br />membrane be used. Even when exposed to ultraviolet light, LLDPE has a <br />functional life of about 12 years before it starts to degrade. Since the liner will be <br />used in an area where ore is stored in piles less than 1 S feet in height and which <br />has low potential for runoff, a 30-mil LLDPE liner membrane represents the <br />minimum acceptable thickness. Please forward the appropriate specifications for <br />this different liner material. <br /> <br />Final Van 4 RTC v2 Letter.doc