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-~ y ~, r ~}e~•: `~ ' ,~_3w. /, +wC ~~y~, { ~~~•r'~r February 6, 1982 TO: Rich Wmingue FROM: Jerry ZZmpfer Inll ail ~.i ..r,Al~ uii r~ulr 11 IM.VI r..rvmrun UEI'AP.T 1rlt NT OF NATIIHAL RESOURCES D. Mnuly Pdscuc, Eantubvn Duccior 425 Centennial Building, 171 Sherman Slr eel Denver, Coloratlo 80200 Tel. i003) 8J9-]567 David C. Shelton Director RE: Predicted Sediment Yield for Trapper Mine, Craig, Colorado 7 have just finished reading a discussion entitled "Criteria for Sediment Yield from Mined Land" which was included in Utah International's recently submitted mine plan application. The method of estimating sediment yield may be summarized as follows: I. The original and interim OSM criterion for sediment volume, 0.2 acre-feet for each acre of disturbed area, was based on research in eastern Xentucky. . 7. Because water is the primary agent of erosion and the principal vehicle for transport of eroded material, sediment yield should be directly related to the arm unt of runoff from an area, ' 3. Total annual runoff in eastern Kentucky and northwestern Colorado respectively, averages 15 inches and 1 inch. Hence the potential for sediment production _ at the Trapper Mine is far less than that possible in eastern Kentucky. 4. On this basis, the design criteria for sediment volume at the Trapper Mine area can be reduced to one-fifteenth the design criterion applicable in eastern Kentucky, (The pro-rated sediment volume criterion at the Trapper Mine works out to 0.2/15 = 0.013 acre-ft/acre of disturbance.) Utah International proposes to adopt a criterion of 0.02 acre-feet per acre of disturbance for sediment volume in the design of sedimentation ponds. The basic assumption that sediment yield should be related proportionally to the artaunt of runoff From an area is fallacious. I have attached a figure taken from Langbein and Schumm (I 958). This figure suggests that the annual sediment yield for the Craig minesite may 6e three times that reported in Kentucky. (cont'd)