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Steriat - 2.05.3 8) Grade bench outslope and surface to final configuration (maximum 2H:1V slopes) 9) Place a rninunum of 4 feet of suitable (non-toxic, non-combustible) cover material on the regraded surfaces and seed to establish permanent vegetation Diversion and collection ditches are designed to safely pass the peak flows from the 100-yraz, 24- hour design storm even[ and include appropriate channel protection, where required, to assure long- termstability and prevent excessive erosion. Maintenance practices include quarterly inspections by a Registered Professional Engineer or his qualified designate, certification on completion of each phase (new fill bench) of construction, clean-out and repair of drainage structures, and additional periodic inspections for any evidence of instability or excessive erosion. Quarterly inspection reporcs note pile conditions, quantity and location of any refuse placed in or removed from the pile, any maintenance or repair activities completed, and the status of any final grading and reclamation activities. Any potentially hazardous conditions identified as a result of the inspections will be promptly reported to the DMG, and emergency mitigation measures implemented as soon as reasonably feasible. East Yard Pile -The GSeam portal bench, where the East Yard pile is located, was constructed prior to 1977 and topsoil was not segregated and saved from this area during portal development. A three- foot layEr of surface material was, however, removed from the portal bench prior to refuse placement and stored in accordance with Section 2.05.3(5) for future reclamation use. This material, which was stored both east and west of the refuse pile area, has been identified for use as an Elk Creek yard soil borrow material The soil material stored on the west side of the pile was hauled to the East Yard soil pile in 1993 in order to enlarge the existing refuse disposal area. This pile was subsequently consolidated with the Elk Cmek soil stockpile during the mine expansion activities. The East Yana pile, as shown on the General Facilities Map, (Map 2.05-M1), is designed to contain approximately 60,000 cubic yards of refuse material The pile was nearing capacity in 1997 prompting OMI to proceed with identification, evaluation, design, and development of the new West Valley coal mine refuse pile. In conjunction with construction of the Elk Creek coal stockpile pad, however, approximately 25,000 cubic yards of refuse was removed from the East Yard pile for use as fill Removal of this material opened up additional available capacity for continued refuse placement in this area. Dependent on operating requirements and considerations, OMI may place coal mine refuse materials in either the East Yana pile or the new West Valley coal mine refuse pile until the East pile reaches capacity. Once the East pile reaches capacity, all coal mine refuse disposal activities will shift to the West Valley area and the East pile will be reclaimed. During final reclamation, the pile surface will be graded to the approximate contours shown on the Facilities Postmining Topography Map, (Map 2.05-M6), and covered with four feet of non-toxic and non-combustible material The 2.1 acre disposal site will require about 13,500 cubic yards of cover material. This cover material will come from excess cut material generated during reclamation of the Elk Creek coal handling, support, and ancil1azyfacilities area. Slope stability analyses were performed for both the existing East and the new West Valley coal mine refuse piles. In general, the nature of the soil profile used in the initial slope stability model for the East pile consisted of refuse material overlying shallow deposiu of colluvium and man-made fill, with a bedrock surface consisting of inter-bedded sandstones, siltstones, and shales. A 4-foot thick layt r of cover material was assumed co cover the refuse material. Material properties were obtained from a review of stability reports from three separate mines in the area. The material properties are summ~n~rd as follows: Mute Material ~ cohesion gamma Red Canyon Mtne Gob 28.5 200 78.8 . North Thompson Creek Wash Plant 34.0 150 82.0 Refuse Blue Ribbon Mine Gob 32.0 SO 73.0 PR04 2.05-46 Revised August 2000