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Vll. Disposal of Excess Spoil - Rule 4.09 <br />The Permit is found to be in compliance with Rule 4.09. Information on excess spoil waste can <br />be found in Sections 2.05 and 4.09 of the Permit. <br />Colowyo Mine has five approved excess spoil fills: Streeter, West Pit, Section 16, East Taylor <br />and West Taylor. Overburden material from the initial box cut for the East Pit was placed in the <br />Streeter valley fill. Now complete, Streeter Fill contains approximately 54 million cubic yards of <br />excess spoil fill. Capacity of the West Pit fill is 16.5 million cubic yards and capacity of the <br />Section 16 fill is 1.5 million cubic yards. <br />Specific information on the Streeter Fill can be found in Exhibit 12 of the Permit and in Section <br />B, Item V of the original findings document. Specific information on the West Pit and Section 16 <br />fills is presented in Exhibit 19 of the Permit and in the files for revision PR -01. The fills meet <br />the regulatory definition of valley fills and therefore must meet the regulatory requirements of <br />Rules 4.09.1 and 4.09.2. <br />In this regard, the Division approved the fills as disposal areas for excess spoil [Rule 4.09.1(1)]. <br />The Division approved fill designs. These designs are found in Exhibit 19 of the Permit. <br />Construction approved was by end dumping excess spoil material in 50- to 100 -foot horizontal <br />lifts. Prior to construction of the fills, all topsoil was removed from the areas as well as clay <br />subsoils beneath the toe of the West Pit fill. Rock underdrains are constructed in natural drainage <br />bottoms from the toes to the heads of the fills. The fills are completed with 3h: Iv outslopes and <br />with 12 -foot -wide terraces constructed at approximately 100 -foot intervals. Topsoil replacement <br />and seeding completes the reclamation. A series of survey monuments and groundwater <br />piezometer wells are monitored quarterly, with results reported to the Division. <br />Based upon the geotechnical analyses prepared by CTL/Thompson Inc. (September 5, 1991 and <br />April 27, 1992) and submitted by CCC and based upon monitoring data from the Streeter Fill at <br />the Colowyo Mine, the Division found that the proposed West Pit and Section 16 excess spoil <br />fills were designed in compliance with the requirement of Rule 4.09.2. Specifically, the fills were <br />designed to attain static safety factors in excess of 1.5. Further, material densities will be <br />adequate to prevent mass movement; end dumped lift placement and gravity segregation of spoil <br />materials will preclude the formation of deleterious voids within the fills; and no contamination <br />of the rock underdrains will occur [Rule 4.09.1(2)]. <br />The use of vegetation and organic material as mulch or as an amendment to topsoil to control <br />erosion, promote growth, or increase moisture retention was approved [Rule 4.09.1(4)]. The <br />locations of the excess spoil fill disposal areas were approved [Rule 4.09.1(6)]. The use of <br />terraces in order to control erosion and enhance stability was approved [4.09.1(9)]. <br />PR -04, Colowyo Coal Mine C1981-019 48 August 2016 <br />