2021-09-07_REVISION - M1973021 (4)

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Aggregate Industries, Morrison Quarry Amendment No.7 to Permit M-1973-021 FYZ Morrison,CO North Repository Area Additional fill placement at the North Repository Area (10.6 acres) is planned to mitigate negative visual impacts from early mining in the area. An engineered fill slope on the western wall near the southern end of the North Quarry will be constructed with byproduct materials generated within the quarry. The area has been used since 1999 and was enlarged in 2005 using a mixture of structural fill and fine-grained soils identified as jade air fines (JAF), with a finished slope of 2H:1 V. The foundation of the toe area of the slope consists of previously placed JAF, and the remainder of the slope is founded on bedrock. Based on the production of byproduct material, the slope will continue to be constructed to an approximate height of 200 feet and has dewatering strip drains located at the base of the highwalls. In January 2007, a toe buttress and underdrain system were constructed in the North Repository Area to improve slope stability and enable placement of additional waste material. The buttress was constructed primarily of waste rock material with small amounts of JAF. Upon completion of the buttress, Aggregate Industries, Inc. subsequently began placement of a mixture of JAF, overburden, and waste rock in the area gained by the buttress construction. In 2009, a final buildout design (provided as Appendix 3) was developed for the North Repository Area and included a 2H:1V slope extending from the existing toe buttress, with two benches of varying widths at El. 6,676 and El. 6,790. The repository has a maximum design elevation of El. 6,920, and the total capacity to store byproduct materials is estimated to be 667,000 cubic yards. For reclamation, it is assumed a 2-foot cover layer will be placed over the final slopes of the repository post mining. Slopes may range from 2H:1 V to 20H:1 V depending on the amount of byproduct material stored in the repository. As detailed in Exhibit F.4, future fill placement in the North Repository Area will be performed in adjacent areas to the north. The benches and upper surfaces will be sloped to allow for surface drainage. Strip drains will be installed at the base of the highwall on all benches and will be placed along the entire length of the bench, daylighting at the northern and southern catch-point lines. Existing strip drains will be extended to daylight beyond the extent of the new fill footprint. Drainage channels, which consist of rundown channels with grouted boulders, will be used to collect and convey surface flow to onsite sedimentation basins. South and West Quarries Reclamation activities in the South and West Quarries focus on reclaiming benches above the anticipated water table at El. 6,500. The West Quarry is defined as the ridge to the west of the Central Quarry. Mining and reclamation activities in the West Quarry will progress from an estimated El. 7,400 to El. 7,000. Anything below this elevation is considered the South Quarry. Phase III Overburden/Topsoil Placement Stockpiled overburden materials and topsoil will be used during reclamation to modify slope geometry and establish vegetation. Topsoil includes the uppermost soil horizon, with limited organic material, and is not abundant on this site due to the steep topography, shallow bedrock, and low precipitation. The onsite soils are formed in-place from parent bedrock and usually do September 2021 1 26