2021-09-07_REVISION - M1973021 (4)

Home Browse Search

Aggregate Industries, Morrison Quarry Amendment No.7 to Permit M-1973-021 FN Morrison,CO not extend deeper than 18 inches below ground surface except near drainages. They primarily consist of stony, sandy loam, which is very low in organic content. The overburden materials consist of the deeper soils and regolith materials (upper weathered and fractured bedrock) and are generally competent for construction, but do not contain organic materials. The overburden materials and topsoil are selectively stockpiled during mining and construction for use during reclamation. Materials for backfill are currently being stockpiled in the Central Quarry, and this operation is planned to continue through the future phases of mining at the South and West Quarries. Stockpiled overburden and topsoil materials would be hauled to the upper quarry benches using the West Quarry Haul Road, which was approved under Technical Revision #7 and is presented in Exhibit D.1. A temporary spur from this haul road will be installed and removed as needed for haul trucks to access the exposed benches of the South Quarry western highwall. As benches become available for reclamation, overburden is placed on the bench surface and shaped and graded in preparation for placing topsoil and hydroseeding. The compacted overburden will slope upward from the access roads at a maximum of 1 H:1V and a minimum of 20H:1V. The steeper (up to maximum 1H:1V) slopes will typically be located on the upper benches of the western quarry highwall, where a significant placement of overburden will be used to improve the visual appearance. Depending upon the amount of overburden that is available during reclamation, the slopes could be backfilled at a significantly shallower slope. As noted in Exhibit F.3, reclamation above bench El. 7,000 will need to follow mining due to access constraints. Unsalable waste material to be used for fill is expected to be encountered in sillimanitic gneiss formations of Phase IV. Benches constructed at 60H:40V above El. 7,000 in Phase III of the South and West Quarries will require volumes of material shown in Table E-1. The highest un-reclaimed bench in the South Quarry is assumed to be at El. 7,400. The highest bench in the West Quarry is proposed to be at El. 7,275. As shown in the Mining & Grading Plan, the Phase III base of the South Quarry is proposed to be at El. 6,500. Table E-1. South and West QuarryPhase III Fill Volumes Quarry Bench Acres Bench Final Rockfall Total Fill Elevation Length (feet Slope Catch (cubic yard) Range per acre) (H:V) Berm West&South 7,400-7,000 20 726 1:1 Eve 3-4 286,815 South 7,000-6,500 77 1,089 10:1 Eve 3-4 1 1089 Total Phase III 1 700,904 Once the surface is prepared, topsoil and natural sediment control measures will be established. Where practical, a bulldozer will track at right angles to the slope to create microtopography in the surface of the topsoil. This has proven effective at Morrison Quarry in slowing erosion, retaining moisture, and catching grass seed. Additional sitework will create swales at right angles to the slope to create a more natural appearing slope. In some locations, the unavoidable, localized, minor rock failures may occur on mined benches, which will serve to further break up the symmetry of mining and create more natural-looking slopes. These have been observed on the El. 6,950 and El. 6,740 benches of the South Quarry western highwall. September 2021 1 27