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• iii iiiiuiiiiiiiiii <br />STAT~OF <br />MINED LAND RECLAMATION DIVISION <br />Department of Natural Resources <br />1313 Sherman St., Room 215 <br />Denver, CO 80203 <br />303 666-3567 <br />FA%:303 832-8106 <br />TO: Jim Pendleton <br />Of CSC <br />Ne~~~~0 <br />Ray Romer, <br />Govamar <br />Michael B. long, <br />Division Director <br />FROM: Allen Sorenson /v~ <br />AE: Time Required to Detoxify Existing Tailings, Battle Mountain Gold, San <br />Luigi Project, File No. M-68-112 <br />DATE: August 10, 1992 <br />I would concur with the conclusion drawn in the memorandum from H rry Posey to <br />yourself dated August 7, 1992, that "one complete cycling of the nterstitial <br />fluids in the tailings solids through the underdrain should remov the WAD <br />cyanide from those interstitial fluids". The question then, is h long will <br />it take for one complete cycling of fluids to occur. <br />The process by which the flow regime within the tailings pile wil transport <br />solutes, in this case WAD cyanide, ie advection. Solutes are tra sported by <br />bulk motion of the flowing interstitial water. Owing to advectio , nonreactive <br />solutes are carried at an average rate equal to the average lines velocity of <br />the water. <br />There is sufficient information in the permit document to allow a etermination <br />of average linear velocity of water within the tails, and to Bete ins the <br />maximum thickness of tailings in the pond at this point in the li of the <br />impoundment. From this information, the calculation on the attac d sheet <br />gives a cycle time of 6.8 years. Because of the phenomenon of by odynamic <br />dispersion, in which some water and solute molecules will travel slower than <br />the average linear velocity, it will actually take some period of ime longer <br />than 6.8 years to completely flush the tailings. I believe that 7.5 years <br />would be a good, conservative, number to work with. <br />It should be of interest to note that because of the conical chap of the <br />tailing impoundment, the lowest 20 feet of the pile comprises onl about 119 of <br />the tailings volume. For this reason, we can utilize 40 feet tailing thickness <br />to calculate the cycle time to detoxify 898 of the tails at 4.5 ye rs. This <br />calculation ie shown on the attached sheet. <br />