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<br />iii iiiiini~iiu ui <br />999 <br />STATE OF CODRADO <br />DIVISIOfV OF MINERALS AND GEOLOGY <br />Department of Natural Resources <br />1313 Sherman 51., Room 215 <br />Denver, CO 80207 <br />Phone'. 13031 866-3567 <br />O~txOl~ @il 8 ~~ $104 9 9 3 <br />W.D. Corley <br />The Corley Company <br />P.O. Box 1821 <br />Colorado Springs, c0 80901 <br />RE:. G.E.C. - Orphan Pit- Coal Revocation Project <br />RN-GOAL-MINES-8 <br />Dear Dr. Corley, <br />pF' e0~ <br />~~ o <br />..~~~ <br />~ l8 T6 <br />Roy Ramer <br />Governor <br />nlichacl 8. Wnq <br />Din Sinn DireUOr <br />The Division received your letter dated September 20, 1443 regarding the hydrology <br />estimates used for the West Pit. It appears that the 10 year 24 hour storm event is <br />between 2.6 and 2.8 inches. The storm event for the 100 year 24 hour event ie roughly <br />3.8 inches. The source of this information is the NOAA Atlas. I am not familiar with <br />the requirement to use a 3.2 inch 10 year 24 hour event which your letter refers to. <br />According to previous calculations conducted by the Division, 2.8 inches for a 10 year <br />24 hour event was calculated for two (2) Newlin Creek culverts. Please note the <br />enclosed sedcad calculations performed February 20, 1993 for the road ditches. <br />The following is a list of references you questioned in your letter dated September 20; <br />CN- 73 CN Source: Table 2-2d TR-66 (enclosed) <br />Watershed Area: 443 acres Source: Rockvale Ouad <br />Elevation: 1,500 feet Source: Rockvale Ouad <br />Time of Con. Programmed by Storm <br />Length of Basin: 12,530' Source: Rockvale Ouad <br />On September 8, 1993 the Division surveyed the West Pit and the Magpie Creek to produce <br />an accurate map of the area. As you suggested in your August 26, 1993 letter, the <br />Division revised the reclamation plan for the West Pit Diversion Ditch to eliminate the <br />pond and reconfigure the drainage. Due to the sudden change in plans, the Division was <br />under time constraints to produce a new ditch design. In order to insure the proper <br />hydrologic length of the ditch and elevation differences, the area was surveyed. The <br />Division took roughly 200 survey points to produce a map for the West .Pit Diversion. <br />David Berry of our office used this map and design parameters in the SEDCAD model to <br />produce a new ditch design for the West Pit. The Division believes this drainage ditch <br />to be a conservative estimate. <br />Please note that Phil Ressler has attached Roll Over Protection Syetema CROPS) on the <br />621 Scraper and the 631 Scraper to comply with OSHA requirements. <br />If you have any questions or need additional information, please call. <br />Sin erely, <br />~-mss <br />Erica S. Crosby <br />Reclamation Special /Project Manager <br />Enclosure (s) <br />cc: David Berry <br />X Larry Routten <br />