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Letter to Ryan J. McHale 2 September 8, 2010 <br />Second Adequacy Review File No. M-2009-076 <br />Based on the forgoing discussion the DRMS has determined that the proposed impoundment will not be <br />approved. Venture Resources and DRMS have briefly discussed the potential to use cemented paste <br />technology to stabilize the tailing, but paste technology may not resolve the liquefaction issue, and would <br />exacerbate the revegetation problem by forming a hard barrier to root penetration. That hard barrier would also <br />create problems for stable placement of topsoil. Further, employment of paste technology would require active <br />dewatering of the tailing prior to or coincident with addition of the cementing agent, which would necessitate a <br />substantial change to the currently proposed mine plan. <br />O w t /1 A n 1 0 '11l 1 ly fling _.CLL '' y /..? L,., 77..1,. 1 1 \\ <br />n 1?lOVerriDer G'+, GI?l, itwile one year since-the uu? vi sue peiii3i? at,pliCalivi7 k>cfcr w 1Ue i.4., (5)). <br />Therefore, the DRMS suggests that the permit application be withdrawn pending the evaluation of alternative <br />impoundment locations (refer to Rule 6.4.20(1)(d)). Alternatively, and as we have discussed, DRMS could <br />issue a permit for limited tailing disposal in Hukill Gulch impounded by conventional earthen damming, such <br />as the barrier bench described in the permit application. In order to gain approval, a technical revision to the <br />permit application must be provided with revised exhibits describing the limited impoundment design and <br />operation. At a minimum, the technical revision must address the following issues: <br />1. The buttressing fill below the concrete barrier wall must be described in terms of engineering properties and <br />fill placement. The DRMS requires that the slope of this fill be no steeper than 2:1, and the slopes of the <br />sediment pond embankment also be no steeper than 2:1. If these sloping requirements reduce the capacity of <br />the sediment pond, revised modeling must be prepared to demonstrate treatment of runoff from a ten year <br />storm. It is stated in Exhibit E that the sediment pond embankment was compacted by a minimum of one pass <br />with tracked or rubber tired equipment; this is insufficient, particularly if tracked equipment was used. <br />2. DRMS has discussed the details of Venture Resources Storm Water Management Plan with the Colorado <br />Water Quality Control Division (WQCD). The agencies concur that diversion of clean water around the <br />sediment pond is preferable. If Venture Resources' preference to discharge the diversion ditches to the <br />sediment pond is based on physical constraints and/or increased cost, provide a description of those limitations <br />and rationale for discharging the diverted water to the pond. Otherwise, provide a plan for diversion around the <br />pond. Another issue that came out of the discussions with WQCD is the need to line the diversion ditches and <br />sediment pond outlet with geotextile or otherwise stabilize the substrate prior to placement of riprap. Provide a <br />plan for substrate stabilization in the technical revision. <br />3. Exhibit D states that partially excavated historic waste rock dumps will not be reclaimed, but will be graded <br />to eliminate potential instability along excavated faces. The DRMS requires that the excavated areas be graded <br />to no steeper than 2:1 and that the graded areas be vegetated. Portions of dumps that have not been affected by <br />excavation or grading can be left as is. Provide an area of dump excavation as a "not to exceed" permit <br />condition, and estimated costs to reclaim the excavation.