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Memo to Erica Crosby 2 January 30, 2007 <br />2na Geotechnical Review Permit No. M-1987-028 <br />compliance with the State Engineer's edict prohibiting retention of storm water for more than 72- <br />hours after a rain or snowmelt event. DRMS has two issues with the Operator's reliance on rapid <br />infiltration in the lower pit. <br />a. Sediment accumulation on the floor of the pit over time would tend to blind off fractures <br />and reduce infiltration. The Operator must commit to cleaning out the lower pit as <br />necessary, and must describe how and where the removed sediment will be disposed. <br />DRMS can approve disposal of the sediment in the waste rock dump, as long as the <br />disposal is well into the interior of the ultimate dump surface so that the sediment is not a <br />slope destabilizing factor. <br />b. For the DRMS to make a finding that storm water will infiltrate the floor of the pit within <br />72 hours, some measurement of the infiltration rate must be provided. The best way to <br />evaluate infiltration would be through a bulk test where a water truck would deliver at least <br />several thousand gallons to the site to be dumped into the pit. Then the known water <br />volume, the measured wetted area, and the time for consumption by infiltration could be <br />used to calculate the infiltration rate. Other smaller scale tests would be less reliable, but <br />would be acceptable to DRMS. There are numerous commercially available permeameters <br />that could be used; there are also borehole based percolation constant head/falling head <br />tests that could be conducted. The Operator should propose a testing method for DRMS <br />consideration, and schedule whatever test that is selected to allow for DRMS to observe the <br />testing if staff scheduling permits. <br />5. The reclamation plan map provided with the CN-O1 application has a 100-foot contour interval. <br />These are insufficient to illustrate reclaimed topography in sufficient detail to portray the direction <br />and rate of slope of all reclaimed lands. The Operator must provide a revised map(s) with a <br />contour interval, and at a lazger scale if need be, sufficient to show details of the final benches and <br />waste dump configurations. <br />6. The Operator is proposing to grade all waste dump out slopes to no steeper than 3H:1 V with the <br />exception of an approximately 2 acre azea below Forest Service Road 228 and adjacent to Taylor <br />Gulch, which will be left at 2H:1 V. In this area, the Operator will use contour furrowing to <br />prepaze the 2H:1 V slope for revegetation. DRMS can approve the 2H:1 V variance for this small <br />portion of the dump, but the variance area must be delineated on the new reclamation plan map to <br />be submitted. <br />7. In the October 12, 20061etter, the Operator provides information on the maximum size of angle of <br />repose dump that maybe in place during the life of the operation. As stated in the June 1, 2006 <br />DRMS memo, these maximum not-yet-graded dump dimensions aze an enforceable permit <br />condition. To look at them otherwise could potentially result in the site being under bonded. The <br />DRMS will use the maximum un-reclaimed dump dimensions in the reclamation cost estimate that <br />will establish the amount of bond to be required. <br />cc: Ken Klco, Azurite, Inc. <br />Cazl Mount, DRMS (via email) <br />c:VJocumenis and Settings~acsUNy DocumentsVily mines rn-01 2vd geotech review.doc <br />