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EERE & AULT <br /> CONSULTANTS, INC . RECEIVE <br /> D <br /> June 14, 2019 JUN 18 z019 <br /> UKXN av ScL%nav <br /> Colorado Mined Land Reclamation Board <br /> 1313 Sherman Street—Room 215 <br /> Denver, Colorado 80203 <br /> Re: Times Mine Bulkhead at Gold Hill Mill Site <br /> Permit No. M-1994-117 <br /> D&A Job No. CG-0788.001.00 <br /> Dear Members of the Colorado Mined Land Reclamation Board: <br /> This letter is written in response to a request by Colorado Milling Company, LLC (CMC)to have <br /> Deere &Ault Consultants Inc, (D&A) comment on Colorado Division of Reclamation, Mining, and <br /> Safety's(DRMS) letter denying the permit amendment for the Gold Hill Mill site (MLRD Limited <br /> Impact 110(2)Permit No. M-1994-117). <br /> D&A was first contacted by CMC on March 7, 2019 to discuss the Gold Hill Mill project with a <br /> specific focus on the Times Mine and associated bulkhead. On March 18, CMC provided D&A with <br /> background information which D&A subsequently reviewed. On April 17, 2019 D&A was <br /> contractually engaged by CMC on to evaluate the Times Mine Bulkhead,a structure on the site used <br /> to store process water in the Times and Wynona Mines. This evaluation was in response to concerns <br /> raised by DBMS in their adequacy review. D&A staff visited the site on April 22, 2019 to make <br /> observations, document conditions, and take measurements. D&A performed the evaluation and <br /> presented the results in a technical memorandum dated May 15, 2019. <br /> On May 21, 2019, DRMS issued Adequacy Review No. 4. The primary issue raised by DRMS in that <br /> letter(review item la) concerns a mine pool drawdown plan should the water level rise above the <br /> design pressure elevation of the bulkhead (8360 ft). Specifically,the letter requests that CMC submit: <br /> A mine pool drawdown plan to rapidly lower water levels in the mine workings in an <br /> emergency situation where bulkhead failure is imminent. This plan should include lowering <br /> water levels, at a minimum, below the collar elevation of the wine connecting the Times <br /> Mine to the Wynona Mine, 8,347.7 feet. The plan should include details such as the type and <br /> location of equipment to be used,pump/flow rate capacities, estimated water volume to be <br /> removed, estimated length of time to drawdown the required water volume, and how the <br /> operation will manage water pumped from the workings (i.e., Will a discharge permit be <br /> required from the CDPHE, WQCD?If so, include in Exhibit F). The mine pool drawdown <br /> plan should also include procedures for evaluating the bulkhead after the mine pool has been <br /> lowered to a safe level. <br /> D&A agrees with DRMS on the need to have a mine pool drawdown plan. The first step in preparing <br /> such a plan is to evaluate the quantity of water in the mine pool at a given elevation above the <br /> Wynona Winze collar(8347.7). Once the quantity of water is known, an appropriate control plan can <br /> be developed. Estimating the water quantity on this site is difficult because the extents and exact <br /> 600 S.Airport Road,Building A,Suite 205 <br /> Longmont,CO 80503 <br /> Phone: 303-651-1468 Fax: 303-651-1469 <br />