2021-04-20_REVISION - M1983033 (20)

Home Browse Search

Walstrum Spur Amendment, Exhibit D— Mining Plan April 2021 30 years. In this manner, diagonal "slices" were mined on the entire vertical face of the mining area precluding reclamation on any given bench until the final slice is removed. Currently the upper five benches of the Existing Quarry are at their final location and have been reclaimed over the past five years. Mining in the Spur Amendment The mining of the Spur Amendment from top to bottom is an important difference from how the Existing Quarry has been mined. By mining from top to bottom, upper benches can be reclaimed after they have been mined. Within the Spur Amendment, according to the Geotechnical Stability Exhibit, slopes can be mined as steep as 0.6H:1V. This slope is measured as an overall average slope from the top to the floor of the mined area. Along each slope, benches will be created. Each slope will consist of a 30- to 100-foot high near-vertical faces separated by 20- to 40-foot wide benches, with an overall average slope that will not exceed 0.6H:1V. To reduce the visual impact of the steep quarry walls, the Operator will slope the more visible slopes (above 8,000 ft) at a maximum average steepness of 1 H:1 V. Adaptive mining methods will be used as mining progresses. Bench heights and widths will be adjusted due to geologic factors encountered during mining such as joint systems, rock types, lateral variations, and fracturing. Benches on the Spur Amendment will be shaped to wrap into the benches in the Existing Quarry as shown on Exhibit F-2. Mining in the Existing Quarry Mining methods in the Existing Quarry will continue as is currently being done. The east side will be mined until a final overall average slope that will not exceed 0.6H:1V is achieved. The north side will be mined and backfilled to an overall average slope that will not exceed 2H:1V. The slope is intended to appear more natural to outside observers viewing from the south. The west side will be mined to an overall average slope that will not exceed 1H:1V. Minin� in all three_areas will begin at the highest elevation and_progress down to the final quarry floor elevation. — — -- -- - - -- -- -- -- Typical mining cross sections of the east, north, and west slope areas are presented in Exhibit C-5. Factors that may impact bench widths and vertical face heights include geologic properties such as joint systems, rock types, lateral variations, and fracturing. As a result, bench widths and vertical face heights are expected to vary. 3.2 Earthmoving 6.4.4(b) earthmoving Earthmoving is performed using a combination of mobile mining equipment including, but not limited to: driils, loaders, excavators, dozers, blades, haul trucks, and water trucks. 3.3 Water Diversions and Impoundments 6.4.4(c) al/ water diversions and impoundments There will be no new water diversions or impoundments associated with the Spur Amendment. Water used for dust suppression and in the aggregate wash plant will continue to be pumped from Clear Creek under a water- court decree and augmentation plan. Stormwater resulting from precipitation falling on disturbed areas of the Spur Amendment will be drained to the Existing Quarry using ditches and topography. Water impoundments consisting of natural ponding areas and detention basins to store and treat stormwater will continue to be used. The active mine level elevation will be sloped to drain from east to west towards the Existing Quarry to utilize stormwater controls already in place in the Existing Quarry. As the Spur Amendment progresses, Best Management Practices will be adjusted as needed to handle stormwater. When necessary, stormwater will be discharged in accordance with the site discharge permit. No stormwater collected will be held for more than 72 hours unless evaporative loss is accounted for in the existing water supply plan. See Exhibit G Water Information for more details on drainage and stormwater runoff. QTETRA TECH P a g e 4 � 9