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iii i~iiii~iiiiu iii 999 STATE OF COLORADO Roy Romer, Gove DEPARTMENT OF NATURAL RESOURCES MINED LAND RECLAMATION DIVISION FRED R. BANTA, Director January 23, 1989 h1r. Dave Stout Environmental Coordinator 141 Union Blvd., Suite 400 P.O. Box 15596 Lakewood, Colorado 80215 Re: Drainage Control and Diversion Structures for Coal Waste Piles Dear A1r. Stout: During the 1988 oversight year, the Federal Office of Surface Mining initiated a special study in reviewing Colorado's approved program. The subject of the study was drainage and diversion ditch design for coal waste piles. During this review it became apparent that drainage and diversion structures for some waste piles were designed and constructed to control a 10 year-24 hour storm event. Colorado regulations require that these types of structures be designed and constructed to safely pass a 100 year-24 hour storm event. Specifically, see Colorado Rules 4.10.3(2) and 4.09.2(7). During our original review, the Division interpreted the regulations such that these structures were treated as temporary diversions only required to pass a 10 year event. These structures were constructed in accordance with the approved plan, however, the Division's interpretation was in error. In order to resolve this problem without the use of enforcement actions, the Division has entered into an agreement with OSM. To ensure that all coal waste piles within the state meet the 100 year requirement, the Division has reviewed the designs for all approved waste piles. All designs must be in compliance by April 30, 1989 with actual on the ground modifications completed by May 30, 1989. Revision of designs by technical revision and on the ground modifications by these dates will avoid the possibility of an enforcement action being taken. Enclosed is a memo which details the specific potential problems related to your mines' refuse disposal area, 215 Centennial Building, 1313 Sherman Street Denver, Colorado 80203-2273 Tel. (303) 866-3567