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West Elk Coal Company, Inc. <br />Posl Ollice Box 591 <br />Somerset, Colora tlo 81434 <br />Telephone 303 929 5015 <br />September 18, 1989 <br />111lllllllll!!l1111 / \ <br />~~(~.' +yy .a ~ ~~~ <br />C G 1 r '~~~ 1 ~~ 1. 4' <br />~~ 1 <br />^~_I7 n~ Tnn~ <br />`~;r <br />^. cr~I -. <br />~'OR <br />Mr. Matthew S. Hayes <br />Colorado Mined Land Reclamation Division <br />1313 Sherman Street, Room 215 <br />Denver, CO 80203-2273 <br />Re: Lower Waste Pile Drainage Control Structures <br />Dear Matt: <br />West Elk Coal Company, Inc. (WECC) and our consultant, <br />Geowest Golden, Inc. have reviewed the designed <br />velocities of the Lower Refuse Pile drainage ditches in <br />the event of a 100-year storm. The designed velocities <br />were compared to the existing ditch configuration <br />velocities to verify the need for riprap in some <br />locations. <br />The ditches that have been constructed are slightly <br />larger than the original design in a trapezoidal shape <br />with a minimum 12-inch wide bottom and approximately 2H <br />to lV side slopes. The actual configuration of the north <br />ditch system resulted in a significant reduction in <br />velocity. This channel now has a maximum velocity of 3.8 <br />fps for a 100-year storm during Phase V and will not <br />require riprap. The north ditch system is the only <br />system which is permanent and will not require further <br />construction for the life of the pile. Regular <br />maintenance will be continued. <br />The east and lower southwest ditches which could have <br />velocities in excess of 6 fps in the event of a 100-year <br />storm are temporary ditches, in that the ditches may be <br />covered or moved during the Phase IV or Phase V <br />development of the Lower Refuse Pile. The existing <br />ditches have shown no signs of excessive erosion, but <br />instead have self-armored or have required regular <br />maintenance to remove accumulations of sediment. <br />WECC proposes not to riprap the east and lower southwest <br />ditches until they are in a permanent location. In the <br />meantime, a monitoring program will be established to <br />inspect these ditches in conjunction with the quarterly <br />pond and refuse pile inspections, as well as after large <br />ANCO-620a <br />