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2019 Plan of Operations Modification American Gypsum Company, LLC <br /> 6.10 Operating Practices <br /> The proposed activities would be a continuation of current mining operations, where a rotomill <br /> grinds shallow layers (approximately 6 inches) of gypsum and intraburden in the active pit. <br /> Gypsum is hauled via 25-ton truck/trailers to American Gypsum's wallboard plant approximately <br /> 1.6 miles south of the Mine entrance. Intraburden is stockpiled or stored on-site, used to construct <br /> access roads, or used as backfill material in progressive reclamation activities. <br /> 6.10.1 Mining Methods <br /> The Upper Pit expansion and the East Pit would be mined using the same methods as used in <br /> the current Upper Pit operations. A rotomill continuous milling machine removes the top surface <br /> of gypsum and intraburden with an active working width of approximately 10 to 12 feet. The pit <br /> floor grades to drain to low area within the pit that temporarily contains surface water runoff within <br /> the pit footprint, with a 2-foot high perimeter berm to provide additional surface water controls. <br /> The rotomill constructs pit slopes at 1 H:1 V, with 10-foot wide benches constructed every <br /> 40 vertical feet. Intraburden is separated from gypsum (based on visual classification between <br /> material types) with a loader and stockpiled on the active pit floor prior to being hauled outside <br /> the pit. <br /> Gypsum is hauled directly to American Gypsum's wallboard plant using over-the-road trucks and <br /> trailers with a 25-ton capacity. Intraburden is hauled to various locations, used to construct roads, <br /> as backfill material in progressive reclamation activities, or stockpiled/stored within approved <br /> disturbance areas. For the East Pit, overburden would be removed prior to active mining, using <br /> existing site access roads while overburden is excavated for use as fill material for the East Pit <br /> Access Road construction. <br /> The Upper Pit and East Pit would be developed to allow for progressive or concurrent reclamation, <br /> where a portion of the completed pit is to be backfilled using overburden or intraburden removed <br /> after gypsum removal. This approach minimizes additional disturbance areas for overburden or <br /> intraburden storage, essentially using completed portions of the pit to store overburden or <br /> intraburden. Where possible, slopes will be backfilled to planned reclamation grades (2.5H:1V or <br /> shallower) to minimize material re-handling. <br /> Although the primary mining method would be rotomills, drilling and blasting may be required <br /> throughout pit development. Periodically, isolated zones of hard anhydrite are encountered during <br /> open pit mining. The rotomill is unable to process the hard anhydrite, requiring drilling and blasting <br /> to continue pit development. In the past 12 years of operation, drilling and blasting has only been <br /> used twice. For the Upper Pit expansion and East Pit development, drilling and blasting may be <br /> used but would be extremely rare. If blasting is required for pit development, blasting agents would <br /> include ammonium nitrate/fuel oil (AN/FO). Blasting would be performed using cast booster and <br /> nonelectric and/or electric blasting caps. Since blasting will be subcontracted, blasting materials <br /> and equipment will not be stored on site; blasting materials will only be on site temporarily during <br /> blasting programs. Proper approvals would be obtained, and any required notifications made prior <br /> to blasting. <br /> Am Gypsum Poo Mod ISSD 20190909 September 2019 [29] <br />