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Mr. Tom Gillis ' <br />December 23, 1981 <br />Page 2 <br />_ 3. From the information presented, it is difficult to ascertain how the <br />figure of 24 cubic feet of sediment inflow was arrived at. However, <br />ARCO has allowed 730 cubic feet of capacity for washdown. This <br />should make the pond sizing adequate to handle the yearly sediment <br />accumulation. ARCO should submit the rationale used in designing the <br />pond. - <br />The sediment volume was determined by the Universal Soils Loss <br />Equation as referenced in the Manual of Erosion Control-Principles and <br />Practice by the Utah Research Lab, June, 1978. The volume of <br />sediment inflow for this area was determined to be eight cubic feet. <br />The pond was sized to handle sediments for three years, thus the 24 <br />cubic feet. <br />The volume of water inflow from a 10-year, 24-hour event was <br />determined by using equations referenced in Procedwes for <br />Determininit Peak Flows in Colorado by the Soils Conservation Service, <br />l.. March, 1977. <br />The volume of washdown was determined by using past practice <br />techniques at ow other operations. <br />I would appreciate receiving confirmation from. you as soon as ossible that we <br />have now fully satisified Stipulation 2 (CMLRD Findings Document) and Stipulation <br />37 (CMLRD Findings Document) since we are planning to begin construction of the <br />loadout facility within tfie next few weeks. -Upon word that we have satisifed these <br />stipulations I will provide you with five copies of. this letter designated as Letter <br />3.3.1.A and revised page 3-46b for inclusion in your copies of the Mt. Gunnison <br />Mining and Reclamation Plan. .:_.~ - <br />The furnishing of this material does not constitute an admission that the same is <br />required by law nor does Atlantic Richfield Company hereby admit that its permit <br />application or the permit granted for the Mt. Gunnison No. 1 Underground Mine is <br />now, or at any time, was in any manner defective, deficient, incomplete or not in <br />compliance with the requirements of law. <br /> <br />• <br />• <br /> <br />