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fills is presented in Exhibit 19 of the PAP and in the files for revision PR -01. The fills meet the <br />regulatory definition of valley fills and therefore must meet the regulatory requirements of Rules <br />4.09.1 and 4.09.2. <br />The Division approved the fills as disposal areas for excess spoil (Rule 4.09.1(1)). Approved fill <br />designs are found in Exhibit 19 of the PAP. The construction method approved was end dumping <br />excess spoil material in 50- to 100 -foot horizontal lifts. Prior to construction of the fills, all topsoil <br />was removed from the areas as well as clay subsoils beneath the toe of the West Pit fill. Rock <br />underdrains are constructed in natural drainage bottoms from the toes to the heads of the fills. The <br />fills are completed with 3h:ly outslopes and with 12 -foot -wide terraces constructed at <br />approximately 100 -foot intervals. Topsoil replacement and seeding completes the reclamation. A <br />series of survey monuments and groundwater piezometer wells are monitored quarterly, with <br />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 Colowyo to the Division, and based upon monitoring data from <br />the Streeter Fill at the Mine, the Division found that the West Pit and Section 16 excess spoil fills <br />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; material densities will be adequate to <br />prevent mass movement; end dumped lift placement and gravity segregation of spoil materials will <br />preclude the formation of deleterious voids within the fills; and no contamination of the rock <br />underdrains would occur (Rule 4.09.1(2)). <br />The Division has approved the following practices related to fills: <br />• Vegetation and organic material can be used as mulch or as an amendment to topsoil to <br />control erosion, promote growth, or increase moisture retention (Rule 4.09.1(4)). <br />• Terraces can be used in order to control erosion and enhance stability (Rule 4.09.1(9)). <br />VIII. Coal Mine Waste Banks - Rule 4.10 <br />The Mine has no coal processing waste banks. <br />IX. Coal Mine Waste - Rule 4.11 <br />No water is used in the coal processing operation, except for dust suppression, and no coal <br />processing waste is produced. <br />Non -coal waste is placed in the backfill of pits in a manner consistent with the requirements of <br />Rule 4.11.4. <br />X. Slides and Damage - Rule 4.12 <br />The Permit is found to be in compliance with Rule 4.12. Because of the mining technique used, <br />Revised Proposed Decision and Findings of Compliance August 2018 <br />Permit Renewal No. 7 P a g e 144 <br />