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RULE 2 PERMITS <br />Nature of the Experimental Practice <br />Colowyo is presently constructing a permanent fill in Streeter Draw. The spoil placed in these fills will <br />not be required to achieve approximate original contour as shown on the Post-mining Topography Map <br />(Map 19) and the Fill Design - Experimental Practice Map (Map 30). <br />Colowyo has undertaken geotechnical engineering studies to demonstrate that spoil pile fills in this area <br />can be constructed with 100 foot lifts, and no durable rock underdrains and still meet or exceed the public <br />safety and environmental protection standards intended by regulation. See Exhibit 12, Experimental <br />Practice Information. <br />Use of the Experimental Practice <br />The alternative method of excess spoil pile construction at the Colowyo operation provides an opportunity <br />to advance technologies of mine fill construction beyond the stringency of existing design criteria to assist <br />in the formulation of a systematic approach to tailor the design standards found in regulations for specific <br />conditions found in the and West. The proven effectiveness of the practice will be an economical savings <br />not only to Colowyo, but ultimately to the consumer. <br />Environmental Protection <br />The location of the excess spoil pile in Streeter Draw is shown on the Existing Structures - South Map <br />(Map 22). <br />The fill structure has been designed so that drainage will not be directed over the outslope and all surface <br />water runoff from the area above the fill will be diverted into designated diversion structures as shown on <br />the Hydrology Map - South (Map 12) and the Fill Design - Experimental Practice Map (Map 30). <br />Runoff will be directed to the sedimentation pond located at the base of the fill. The remaining fill to be <br />placed in Streeter Fill will be placed in lifts not to exceed 100 feet. Detailed geotechnical work has been <br />performed on the Streeter Fill to evaluate and ensure stability. The results of these studies are discussed in <br />Exhibit 12, Experimental Practice Information. The fill will be constructed so as to blend in with the <br />existing topography and the average slope outslope of the fill will be approximately 3:1 (horizontal to <br />vertical) topsoiled and will be revegetated according to Section 2.05.4. Mulching and contour furrows as <br />described in Section 2.05.4 have been utilized for erosion control in conjunction with benches on the area <br />of the Streeter Fill that has been completed. Benches have been constructed every 100 vertical feet from <br />the base of the fill at 6600 feet to the 6900 foot level. These benches are 30 feet wide with a 10 percent <br />slope toward the face of the fill. From the 6900 feet level to the completion of the fill at elevation 7225, <br />the fill will be graded to an overall 3:1 slope, and will be controlled by the use of mulch, contour furrows, <br />and/or benches. If benches are used, they will be 20 feet wide, or less, and will slope towards the face of <br />the fill at 5%. The hydrologic calculations for the benches and contour furrows are included in Exhibit 7, <br />Hydrologic Information. <br />Prior to depositing any fill on the disposal site, topsoil was removed, segregated, and stored or <br />redistributed as explained in Sections 2.05.4 and 4.06. <br />The site selected for the disposal of the excess spoil was chosen with the intention of maximizing coal <br />recovery and minimizing the amount of disturbed area. The site represents a stable area available for <br />disposal and was chosen in order to avoid affecting additional drainage areas. This selection for the <br />excess spoil disposal site minimizes the total affected acreage by avoiding the disturbance of otherwise <br />undisturbed drainage basins. <br />Rule 2 Permits 2.06-4 Revision Date: 6/23/08 <br />Revision No.: MR-91