_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 | 19 will be occur between El. 6,600 and El. 6,500. As mining operations approach these elevations, monitoring well data and other hydrogeologic data collected in the South Quarry (refer to Exhibit G – Water Information), in conjunction with visual observations, will be used to determine final bottom elevations throughout the quarry. As groundwater levels vary in different areas of the South Quarry, it is anticipated that corresponding bottom elevations may also vary. If groundwater is encountered during mining, operations will cease in that area and the excavation will be backfilled and sealed. South Quarry mining activities will initially focus on lowering existing western, southern, and eastern benches of the quarry to maximum depth before groundwater is encountered. Once the West Quarry development is complete, mining will proceed on the northwestern and northern faces of the South Quarry to maximum depth before groundwater is encountered. Throughout the South Quarry, for areas below El. 7,000 and above El. 6,600, the maximum highwall height will be 60 feet, and the minimum bench width will be 40 feet (40H:60V). To support incorporating future benches into existing benches, alternative, less aggressive configurations may be mined. For areas below El. 6,600, the maximum highwall height will be 60 feet, and the minimum bench width will be 40 feet (60H:40V); however, mining will not proceed steeper than an 40V:40H configuration until stability analyses demonstrate a FOS greater than 1.25 and a technical revision is submitted to DRMS for review and approval. Temporary spur roads from the West Quarry Haul Road will re-establish access to the upper benches of the South Quarry western slope up to El. 7,400. Benches above El. 7,000 will be reclaimed promptly to address visual impact concerns. Once completed, South Quarry reclamation activities will continue in a manner that minimizes open benches in accordance with Exhibit E – Reclamation Plan. West Quarry Development Once the West Quarry Haul Road is completed, development of the West Quarry will begin, starting with an upper elevation at approximately El. 7,400 and proceeding down to approximately El. 7,000. For benches above El. 7,000, the maximum highwall height will be 40 feet, and the minimum bench width will be 60 feet (60H:40V). Overburden materials from these upper benches will support remaining upper bench reclamation on the South Quarry western face from El. 7,400 to El. 7,000. Mining in the West Quarry will proceed from west to east (uphill to downhill), terminating at approximately El. 7,000. Mining below this elevation will be considered part of the South Quarry operations. Reclamation of the West Quarry benches will be conducted concurrently as mining proceeds on the lower benches to reduce the duration of visual exposure. Water Management To manage surface water runoff into the South Quarry, runoff from UD#1 will be permanently diverted to UD#2. The drainage diversion structure will be constructed concurrent with the South Quarry West Wall El. 7,000 bench reclamation. It is anticipated that construction of this diversion structure will be completed in early 2022. The drainage diversion structure consists of an open culvert and two detention basins: one at the culvert inlet, and one at the UD#2 culvert