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• • III IIIIIIIIIIIII III 999 STATE OF COLORADO DIVISION OF MINERALS AND GEOLOGY Department of Natural Resources oe~co~ 1313 Sherman St., Room 215 N~~ ~~~~jjj Denver CO 80203 • ~ ~h , • Phone (303) 866-3567 ' ~e~a' FAX: 1303)832-8106 Ruy Rumcr Gnvernur Michael B Long Division Director DATE: August 24, 1993 TO: Janet Binns FROM: Susan Burgmaier ~,~6 RE: Hayden Gulch Loadout (C-92-081) Technical Revision 1 I have reviewed the culvert and ditch designs submitted with the above mentioned technical revision. For the most part, it appears that all of the culverts and ditches will convey a 10 year - 24 hour storm event. I do, however, have a few concerns. Prior to approval of the designs, the operator should address the following: 1. Based on the estimated water velocities entering culverts LFC-2, LFC-3, and LFC-4, it would appear that some inlet protection is necessary. HGTI should commit to visual monitoring of all culvert inlets and outlets, and to providing channel protection where necessary. 2. The ditch designs submitted do not include an allowance for .3' of freeboard, as required by Rule 4.05.3(7)(b). HGTI should verify that all constructed ditches include .3' of freeboard, and include the designated freeboard in the designs. 3. Some portions of the SEDCAD output sheets were missing. Please have HGTI resubmit the following: LFC-3A - SUBWATERSHED/STRUCTURE INPUT/OUTPUT TABLE LFC-3A -DETAILED SUBWATERSHED INPUT/OUTPUT TABLE LFC-3A -NON-POND STRUCTURE INPUT/OUTPUT TABLE LFC-7 -DETAILED SUBWATERSHED INPUT/OUTPUT TABLE 4. HGTI uses a rainfall depth of 1.6 inches for the 10 year - 24 hour storm event. The NOAA Atlas 2, Volume III shows a depth of 1.7 inches for the Hayden area. Peabody Western Coal Company used a depth of 1.6 inches for designing structures at the Seneca II Mine, which we also questioned. We are in the process of resolving this