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CIVIL RESURCES, LLC <br /> ENGINEERS & PLANNERS <br /> MEMORANDUM <br /> TO: Project File <br /> FROM: Civil Resources, LLC <br /> DATE: October 30,2018 <br /> RE: Inouye Gravel Mine,M2018-037—Slope Stability Discussion(Excavation Slope Change) <br /> This memo summarizes the change from a 0.5 horizontal to 1 vertical (0.5Hto1V) mining slope to a 3 horizontal to 1 vertical <br /> (3H:1V) mine slope. An extensive slope stability analyses was performed showing the slopes and setbacks are safe for the <br /> original mining 0.5H to 1V slope per Division of Reclamation Mining and Safety(DRMS)guidelines. The miner will change the <br /> proposed mining method to mine at a shallower 3H:1V slope to limit reclamation costs and give themselves the flexibility to <br /> sell or use the overburden onsite or for other gravel mines they own and operate. <br /> Slope Stability is the method the engineer uses to determine if the slopes will slough or fail as a result of the driving force and <br /> the counteracting force. This is why full below grade reservoirs are very safe because the water inside the below grade <br /> portion of the reclaimed mine counteracts the driving force from the pushing/sloughing slope. The engineers provide <br /> recommendations based on the onsite materials, geotechnical investigations and their overall familiarity of the mine and <br /> mining methods. Typical methods of mining are steep slopes which require greater setbacks and further reclamation. <br /> Shallow slopes require less of a setback and can be reclaimed as they were mined requiring less maintenance and less of a <br /> tendency to slough. The miner will change the method of mining to a shallower 3H:1V slope. This slope is significantly safer <br /> than the 0.5H:1V slope especially when the mine highwall (the initiation point the miner starts to excavate) does not move <br /> back towards any structures. By mining a shallower slope the counteracting forces pushing against the sloughing soil are <br /> greater and therefore are safer than a steeper mine slope. A figure has also been attached depicting this. <br /> 323 FIFA-I STREET • FREDERICK, COLORADO 80530 • PHONE: 303.833. 1416 • FAX: 303.833.2850 <br />