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RECEIVE <br /> LOVELAND 3U� 17IM <br /> READY-MIX DNISIONOFRp ENION <br /> June 14, 2022 MINING AN <br /> CONCRETE <br /> PO BOX 299 Mr. Brock Bowles <br /> LOVELAND, CO 80539 Colorado Division of Reclamation Mining and Safety <br /> 1001 E 62"d Avenue <br /> OFFICE 970.667.2680 Room 215 <br /> FAX 970.667.0092 Denver, CO 80216 <br /> RE: Knox Pit M2017-036,AR-1 <br /> Request for Technical Revision TR-1 <br /> Dear Brock, <br /> Included with this letter is a request for a Technical Revision (TR)to the Knox Pit <br /> Permit along with a check for$216 for the TR fee. <br /> This TR modifies Exhibits C and F to clarify the general backfill detail and how it will be <br /> constructed; specifically the location of the drain and the liner key in the bedrock in <br /> relation to the compacted backfill for the pit liner. Exhibit E in the current permit <br /> details the implementation of the drain and the compacted clay liner during <br /> reclamation, and supports this modification: <br /> "Placement of the fine grained material will form a low permeable barrier <br /> around the pit boundary with the effect of isolating the pit excavation from the <br /> adjacent groundwater system and to prevent leakage of any water stored in the future <br /> reclaimed pit. Construction of the low permeability barrier...will include placement of <br /> material in successive lifts(typically 1 foot)with concurrent compaction to 95% <br /> Proctor density of each lift as placed. The first lift would be keyed into the Pierre <br /> shale bedrock. Wall thickness of the constructed lining would be typically greater than <br /> 6 feet thick as limited by the capabilities of the equipment used for compaction. Side <br /> slopes of the lined pit would be constructed so as to ensure slope stability." <br /> "Between the low-permeability barrier and surrounding alluvium, a perimeter drain <br /> will be placed in a drain sand. The drain sand will be engineered to prevent migration <br /> of fines into the drain." <br /> The Groundwater Study, 2"d Submittal, in the Permit lays out the intent for the design <br /> and installation of the drain and the compacted liner: <br /> "A perimeter drain will be placed along the outer perimeter of the excavation <br /> that will serve during mining to dewater the toe of the high wall to maintain stability, <br /> and direct groundwater to the dewatering sump. As reclamation materials become <br />