_REVISION - M1973021 (3) - Laserfiche WebLink

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Aggregate Industries, Morrison Quarry Amendment No. 7 to Permit M-1973-021 Morrison, CO October 2021 | 32 planned to be channeled to UD#2 (described in section titled Stormwater and Erosion Control Features, above), it is assumed that UD#3 (previously UD#1 prior to mining) would be able to handle additional stormwater flow generated solely within the South and West Quarries. Until such time that appropriate hydrogeologic and geotechnical investigations are performed and the horizontal drain can be designed and installed, active pumping within the Phase III area of the South Quarry would continue to discharge to Drainage Outfall 003. Grading Grading of fill material will be performed on all benches meeting the requirement approved in Section 5.03 of AM05. In general, fill material will be graded to slopes appropriate to the soil type and terrain of the area. Slopes will be graded to minimize erosion and to facilitate revegetation. Depending on the stability of the rock face encountered, some portions of the high walls may remain exposed, providing nesting habitat for bird species. The graded slopes will vary between 20H:1V and 1H:1V along the reclaimed benches. Final grading will create a surface that is variable and somewhat irregular to give a more natural appearance, while effectively conveying drainage. As recommended in Appendix 1, Rule 6.5 Geotechnical Stability Exhibit, in South and West Quarry benches above El. 7,000 where topsoil backfilling and revegetation is permit-required, several rockfall benches should be left open for rockfill catchment. The Geotechnical Stability Exhibit recommends this consisting of a 5- to 10-foot zone free of fill material every three to four benches. This material-free zone would reduce the potential for isolated rockfall from traveling down slope and propagating down to the active mine areas, reducing the risk to mine personnel and infrastructure. These rockfall berms would remain in place following reclamation for the protection of wildlife and maintenance personnel accessing the former highwall areas. The berms serve a dual purpose as rockfall catchment and a berm against the outboard (downhill) side of access routes crossing the quarry slopes. Quarterly scaling of final slopes will reduce the potential for overhead hazards. Machine scaling will identify instability in rocks within the highwall and will remove the hazard utilizing various techniques under a controlled environment. Prior to final grading and during the vegetation establishment period, catchment berm areas would be cleared of accumulated rockfall to allow for vehicle access. Benches will be constructed at contour intervals described above and will be sloped with grades no steeper than 2H:1V. All fill material will be placed as follows: • Placed in loose, horizontal lifts not to exceed 30-inches thick, based on the maximum particle size of the fill materials; maximum rock sizes are limited to two-thirds of the lift thickness • Compacted to achieve greater than 95% of the maximum dry density determined in accordance with ASTM D698 and specified in AM05 • Placed in a manner that allows for a moisture content within 3% of optimum based on ASTM D698