2009-09-14_REVISION - C1981019 - Laserfiche WebLink

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4.09.1 and 4.09.2. The Division approved the fills as disposal areas for excess spoil [Rule 4.09.1(1)]. Approved fill designs are found in Exhibit 19 of the Permit. The construction method approved was end dumping excess spoil material in 50- to 100-foot horizontal lifts. Prior to construction of the fills, all topsoil was removed from the areas as well as clay subsoils beneath the toe of the West Pit fill. Rock underdrains are constructed in natural drainage bottoms from the toes to the heads of the fills. The fills are completed with 3h:Iv outslopes and with 12-foot-wide terraces constructed at approximately 100-foot intervals. Topsoil replacement and seeding completes the reclamation. A series of survey monuments and groundwater piezometer wells are monitored quarterly, with results reported to the Division. Based upon the geotechnical analyses prepared by CTL/Thompson Inc. (September 5, 1991 and Aw_?__eea _r A 1 t /?\ and 1. t 1 o the Operator and b- 1 data 'from the Streeter April 22r?7, i I\yy!\z? and submitted by the Operator and ased upon rnoni tonng data 'from the Ste Fill at the Colowyo Mine, the Division found that the proposed West Pit and Section 16 excess spoil fills were designed in compliance with the requirement of Rule 4.09.2. Specifically, the fills were designed to attain static safety factors in excess of 1.5; material densities will be adequate to prevent mass movement; end dumped lift placement and gravity segregation of spoil materials will preclude the formation of deleterious voids within the fills; and no contamination of the rock underdrains would occur [Rule 4.09.1(2)]. The use of vegetation and organic material as mulch or as an amendment to topsoil to control erosion, promote growth, or increase moisture retention was approved [Rule 4.09.1(4)]. The locations of the excess spoil fill disposal areas were approved [Rule 4.09.1(6)]. The use of terraces in order to control erosion and enhance stability was approved [4.09.1(9)]. Two additional valley fills and two temporary overburden stockpiles were approved for the South Taylor area through Permit Revision 02. The permanent fills are the West Taylor Fill and the East Taylor Fill. The temporary overburden stockpiles are TS West and TS East. The information on the new valley fills is contained in Permit Volume 12 in Sections 4.09, 4.10, 4.11, 4.12 and 4.13. The West Taylor fill is a valley fill that will be located in the upper west fork of Taylor Creek. It will contain approximately 10 million cubic yards of material from the initial box-cut for the South Taylor Pit. The fill will have a durable-rock drain that will be build by gravity sorting of dumped overburden materials. The initial construction of the fill will be accomplished by wing- dumping material to establish the base of the fill followed by end-dumping of material to complete the fill. Lifts of no more than 100 feet are proposed for the West Taylor Fill. Colowyo proposes to use terrace ditches to divert water off of the face of the fill and to the relief drains on the side. Additionally, 100-year diversion ditches will route clean-water around the fill. Upon completion of the West Taylor Fill the area will have the topsoil replaced and it will be revegetated per the approved reclamation plan. Proposed Decision and Findings of Compliance 14 September 2009 Permit Renewal 05 Page 51