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w"" iii iiiiiiiiiiiiiiii 7 ERIGIFdEERIiLG d4 SUFiVEYIFdG COI! ~9PAi~Y BOX 674 443 DODGE DL=LTA, COLOfiADO. 59416 303-574-7593 '~~~:7RTJLVM1A ~SO~Y~I~'RSZ'•Cl']2 ':' "~'Itaj'-...] 10179 October 22, 1981 19estern Associated Coal Corp. Suite 2300 410 Seventeenth Street Denver, Colorado 00202 ATiN: 19illiam S. Tate Re: Blue Ribbon f-0ine, Ocnch Stability, Violation 01-10 In response to your letter dated July 20, 1901~Lo the F1LR regarding drainage on the above referenced bench, we submit the following design recommendations for your consideration.. Surface runoff, or accumulation of water on Lhe bench itself should be handled with surface ditches much as you presently have them constructed. A gradient should be accomplished from the intersection of the bench with the highwall sloping outward to a point approximately 15 to 20 feet from the outside limits of the bench. Another gradient should be constructed from Lhe berm along the outside edge of the bench back toward Lhe interior of Chc bench to intersect the gradient mentioned above. This will create a very shallow "V" ditch that will convey runoff generated on Lhe bench to appropriate ditches. The drainage, "V" ditch, will be only a few tenths of a foot deep and will permit operation of cyuiprncnt and vehicles with no discomfort to the operator or impairment of the operability of the various pieces of cyuiprncnt. Note that the bench is not flat. At, or near, your present loadout facility, the bench has a break in slope Surface v+ater north of Chis break in slope flows northerly, and surface water south of Lhis point flows southerly. Take advantage of this natural break in slope to com'ey that portion of surface water on the north portion of tf~e I~ench to the 10-inch pipe presently installed in the existing drainage. South of the break in the bench slope, all water can he conveyed to the existing ditch located on the inside shoulder of your access road. Our recommendations for the drainage system to be installed a]ong the outer region of the mine bench, in ^ccordance vrith your July 20, 1981 letter to F1LR, includes several engineering details. {!e have prepared a drawing, which is enclosed, that shows surface drainage as proposed, an assumed line v+here Lhe fill intersects the natural slope, location of the proposed drainage trench, and a cross- section and profile of the propused drainage trench. On Lhat drawing we have reconstructed :rn assumed cunLuur line fur Lhe location of the original hillside.