2016-08-29_REVISION - M1985001 - Laserfiche WebLink

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Grossf ire CSC, en ts Integrated Energy Services May 23`d 2016 Re:Highwall design for Helmericks Pit To whom it may concern: This letter and accompanying Phasing Maps constitute my recommendation. I made a site visit to the pit earlier today and discussed the method of construction with Crossfire Aggregate Services's General Manager, Jay Nielson. I observed the excavated faces in several areas. There was a layer of sand close to the Pit floor which is the top of a shale layer. This varied but was about 5 to 10 feet above the pit floor. Because of the proximity to the pit floor this layer was not a concern. Above that was a sandy loam layer. About 10 to 30 feet off of the pit floor. While trying to take a sample of the material,I noticed it was very hard and dry. I was not able to scrape a sample out of the excavated face very easily. The material had a moderate cemented quality. A visual and tactile examination of the material placed it as a sandy loam with ample rocks embedded in the layer. Above that was a layer with more clay. This layer extends from about 30 feet above the pit floor to the overburden layer. I observed walls of material that were holding vertical integrity up to 40' in height. The wall should be benched so the vertical walls are no higher than 40' with a safety bench of 20' minimum width. An important part of the design is the Excavation Phasing. This phasing is designed for safety during the material extraction process. There is limited time that equipment will be within 20' of the vertical Highwall. Daily inspections, as typical to the industry,will be made of the condition of the wall. Once the excavation of Phase 2 has gotten 60' away from the lower section of the Highwall,the reclamation of Phase 3 and Phase 4 will commence without delay. Sincerely, p0 tic�- Debbi Michal, P.E. ;0 3135 r'• Project Engineer 7:�: FeT9 q� Crossfire,LLC oX, NAL 820 Airport Rd,Durango,Co 81303 p(970)8844869 f(970)403-1129