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Memo to Berhan Keffelew <br />Animas/Helen Waste Pile Rev. <br />page 2 <br />I do have one non-geotechnical concern, which I believe deserves further <br />consideration. The applicant proposes an unterraced facial slope for the <br />amended pile design. I am concerned that this may lead to excessive surface <br />erosion due to runoff from the pile. On page 466 of the revised application <br />the operator states: <br />"Based upon experience at other sites in Colorado, terraces tend to <br />concentrate runoff, resulting in increased erosion, downcutting of <br />channels and associated maintenance work." <br />The Division does not concur with this statement. The applicant should submit <br />appropriate documentation to support this opinion. <br />Further, on pages 467 through 468 of the amended application the applicant <br />states: <br />"This design provides uniform, gentle slopes which will eliminate the <br />concentration of runoff and will alleviate previously experienced erosion <br />problems at the site." <br />While the terraces are not necessary for structural stability, I am concerned <br />that their elimination will result in increased surface erosion. It is <br />extremely difficult, due to equipment operations and waste material <br />consolidation, to maintain a "uniform, gentle slope". Runoff concentrates in <br />settlement troughs and equipment tracks, resulting in local erosional <br />problems. I recommend that you scrutinize this design aspect closely. <br />cc: Savage <br />Doc. No: 3457E <br />