2023-01-05_REVISION - C1981019 (13)

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• The temporary East Taylor Fill - 39 million cubic yards • The permanent West Taylor Fill - 28 million cubic yards • The temporary West Taylor Fill - 12 million cubic yards. The Little Collom Gulch Fill contains the initial box-cut material from the Collom Pit. The fill is also associated with part of the Collom Spoil Pile construction. The approximate design volumetrics associated with these fills are as follows: • The permanent Collom Spoil Pile— 17.3 million cubic yards • The permanent Little Collom Gulch Fill —4.1 million cubic yards • The temporary Collom Spoil Pile —6.6 million cubic yards Specific information on the Streeter Fill can be found in Exhibit 12 of the PAP and in Section B, Item V of the original findings document. Specific information on the West Pit and Section 16 fills is presented in Exhibit 19 of the PAP and in the files for revision PRO1. The fills meet the regulatory definition of valley fills and therefore must meet the regulatory requirements of Rules 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 PAP. The construction method approved was end dumping excess spoil material in 50 to 100foot 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:ly outslopes and with 12footwide terraces constructed at approximately 100foot 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 April 27, 1992) and submitted by Colowyo to the Division, and based upon monitoring data from the Streeter Fill at the 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 Division has approved the following practices related to fills: • Vegetation and organic material can be used as mulch or as an amendment to topsoil to control erosion, promote growth, or increase moisture retention (Rule 4.09.1(4)). • Terraces can be used in order to control erosion and enhance stability (Rule 4.09.1(9)). VIIL Coal Mine Waste Banks - Rule 4.10 Proposed Decision and Findings of Compliance January 5,2023 Permit Renewal No. 8 Page 147