1995-05-26_GENERAL DOCUMENTS - C1981017

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STATE OF COLORADO DIVISION OF MINERALS AND GEOLOGY Department of Natural Resources 1313 Sherman St, Room 215 Denver,Colorado 80203 Phone:(303)866-3567 FAX:(303)832-8106 DEPARTMENT OF NATURAL DATE: February 22, 1995 RESOURCES Roy Romer TO: Steve Renner Governor FROM: Susan Burgmaier o James S.Lochhead Executive Director Michael B Long RE: Coal Basin Mines (C-81-017) Division Director Per your request of Susan McCannon, I have prepared designs for ditches at the Coal Basin Mine complex. The designs I was able to complete were upland diversions for the Rock Tunnel Pile and the Old Refuse Area. For both designs, the only information I had was what is available in the permit application package. Obviously, this may not reflect current site conditions. If site conditions are major departures from the what was approved in the permit application package, the designs would likely not be valid. Following are the required designs, and a summary of assumptions made in their development. Rock Tunnel Pile Diversion The location of the proposed ditch is shown in red on Map II-B-App.3-3, which you furnished to facilitate my review. I tied the new diversion into the lower portion of the existing diversion. In order to arrive at the location of the ditch, I assumed the existing pile edge was where I have shown the ditch. If the pile edge is not at this location, then the ditch design may not work. It will not work if the pile is lower and further north than I have indicated, as there will be more area to divert than I have considered. I assumed there would be 42.01 acres of upland area to divert. The upland area diverted is shown in red on Map II-H-1, provided by you. This same map was used to estimate a time of concentration for runoff, and a curve number assignment for the runoff coefficient. I assigned the upland area a curve number of 56. Assumptions leading to this value were: the soil type, taken from Map III-G-1 is a sandy loam the vegetation type, taken from Map II-H-1, is spruce/fir forest and parkland the estimated cover is 60%-70%, as per Tony Waldron, using available photographs. He did not have any quantitative data available to make this estimate. This value could be more accurate with actual sampling data from the area. These factors were used to get a curve number from the publication "Peak Flows in Colorado", Figure S3 on page 22. I divided the ditch into three sections, according to gradient. Those segments are marked on Map II-B-App.3-3. It appears that Segment 3 has already been constructed. If it meets the minimum design criteria below, it could be left as is. The length and slope of each segment is as follows: Segment 1 - 400', 6.25% Segment 2 - 1100', 12% Segment 3 - 400', 8.75%