2022-10-19_PERMIT FILE - C1981018A (3)

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TR-74 (4/2022) IV-18 The merging of RA-2/3 and RA-4 began during the summer and fall of 1998. Map 76 shows how refuse lifts are constructed. Refuse is dumped in the area being filled and spread in layers to dry. After drying, the refuse is built into layers not exceeding two feet and compacted to 90 percent of maximum dry density (AASHTO Spec. T99-74) as required by Section 4.10.4. The refuse material has to dry out before it can be compacted properly. During the winter months or at times when the material cannot be properly spread and compacted, the refuse material may be temporarily stored on top of the refuse piles. Storage of refuse material in temporary piles will not exceed 300,000 tons at any one time. Tests shall be performed on the waste bank to ensure the minimum level of compaction is reached. These tests shall be made in areas that represent the area being compacted. No test will be performed during periods of rain, snowmelt or when the pile is unreasonably wet. Tests shall be performed on a minimum of a monthly basis during the active compaction process of the refuse pile construction. The tests shall be performed with a nuclear density meter. During the early phase of mine permitting when no actual refuse material was available for testing, the refuse strength and stability characteristics were assumed based on typical scenarios at other sites. Once the actual refuse became available, Western Fuels-Utah (now BME) contracted Lincoln DeVore Laboratories to develop a Proctor curve of the material. Nuclear density equipment was purchased to verify required compaction results. It was found that the original assumptions were quite conservative compared to the actual data. Based upon the actual data, the safety factor exceeds 1.5 using a slope of 3(h):1(v). This factor will be significantly higher for a slope of 4(h):1(v) and 5(h):1(v) as stipulated in the permit. A letter dated January 30, 1987 from Mike Weigand, Chief Engineer at the Deserado Mine supporting the above findings is included as Illustration 42. Additional strength tests on the refuse and stability analysis with a 4:1 slope were conducted by Lincoln-DeVore, Inc. of Grand Junction. The static safety factor was calculated to confirm that it exceeded 1.5. A letter from Lincoln-DeVore is included in Illustration 42A. In 2004 additional cores of the refuse were tested for strength and stability. Based on the new data, Lincoln DeVore concluded that the refuse piles would be adequately stable at 3(h): 1(v) and 200 feet in height. This report is included in Illustration 42B. Huddlesone-Berry, Inc., of Grand Junction performed a geotechnical investigation of the proposed RP-A area and analyzed the stability of the refuse pile slopes. Every scenario in the analysis resulted in a factor of safety well over 1.5. The report is included as illustration 42C. Most of the sedimentation ponds in the Refuse Disposal Area will be a combination dug-out or in-situ and embankment type. This design was chosen because of layout and construction considerations. Soils in this area are mostly Turley fine sandy loam and Moyerson silty-clay. The Moyerson soils have properties suitable for dam embankment construction. Where ponds are constructed in in-site materials not suitable for pond construction, suitable materials will be imported