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<br />,- <br />'~ <br />STATE OF COLORADO <br />DIVISION OF MINERALS AND GEOLOGY <br />DeUanmenl ul Naniral Resources <br />131 J Sherman Sl.. Rouen 215 <br />Denver, Calorarlo AO?03 <br />Phone: 131131 A66-3567 <br />FTX: 130.3) 832-N 106 <br />DATE: NOVEMBER 21, 1996 <br />~~~ <br />DEPARTMENT OF <br />NATURAL <br />RESOURCES <br />Roy Rnmer <br />Governor <br />TO: DAVID HBRRY <br />FROM: JOS DIIDABH ~~ D <br />lames S Lochhead <br />Executive Director <br />Michael B. Long <br />Division Diecor <br />RS: COAL MINE WABTS BANR PRELIMINARY DSBIGN, BANBORN CRSBR <br />MINE, PERMIT NO. C-81-022, ORHOW CARBON AND MINERALS, <br />INC. <br />I have finished my review of the surface water hydrology for the <br />above-mentioned submittal. I have the following questions or <br />comments: <br />The Division suggests that, in order to avoid confusion, the <br />October 1996 report by Westec, entitled "Coal Mine Waste Bank <br />Design For The Sanborn Creek Mine" be purged of possibly <br />unneeded information. In Appendix B, the reach summaries for <br />the 10 year-24 hour event and for the 25 year-24 hour event <br />appear to be unnecessary, since the ditch designs are based <br />solely on the 100 year-24 hour event. Unless there is a reason <br />for including all of this material in the submittal, please <br />consider removing this material from the submittal. <br />Another area of concern is having 100 year-24 hour ditch <br />designs in Appendix B which are superseded by differing 100 <br />year-24 hour ditch designs in Appendix C. The Division assumes <br />that the sole purpose of having the 100 year-24 hour ditch <br />designs in Appendix B is that it shows the combined peak <br />discharge for those ditch reaches which have combined <br />subwatershed flows. However, this information already is shown <br />in the hydrograph summary table in Appendix B. Unless needed, <br />please consider removing the 100 year-24 hour reach summary in <br />Appendix B, or adding a note to that summary that the ditch <br />designs are being superseded by ditch designs in Appendix C. <br />2. For the sake of clarity, the Division requests that an <br />explanation be included, on the page in Appendix B of the <br />Westec report that has the hydrograph summary for the 2.8 inch <br />100 year-24 hour storm event, which describes which <br />subwatershed peak flows contribute to each hydrograph number <br />and to each ditch reach. <br />