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;. <br />r_ <br />~II II~II~II~~~~~ ~I~ <br /> STATE OF COLORADO <br />DIVISION OE MINERALS AND GEOLOGY <br />Department o(NaWral Resources <br /> <br />1313 Sherman St., Room 215 ~ <br />Denver, Colorado 80203 I~~~ <br />Phone: (303) 866-3567 <br />FA%: (3031 832-81 06 <br />DEPARTMENT OF <br /> NATURAL <br />September 7, 1994 RESOURCES <br /> <br />Bryan J. Archer Ray Rome. <br />co~emn. <br />Sun Coal Company Ken Salazar <br />10200 West 44th Avenue, Suite 120 ExerNfveDnea°, <br />Wheat Ridge, Colorado 80033 Michael 8. long <br /> Division Dueaur <br />RE: Meadows #1 Mine (C-81-029) <br />Technical Revision 16 <br />Dear Mr. Archer: <br />This letter serves to reiterate our recent discussions regarding the above mentioned revision. <br />The revision was submitted to correct a permitting defect identified during the May 23 and 24, <br />1994 Division inspection of the site. During that inspection, it was noted that the northwest <br />sediment trap did not appear to be in compliance with current impoundment regulations (Rule <br />4.05.9). Among the deficiencies cited were the absence of construction certifications, and an <br />open channel emergency spillway. The construction certifications were forwarded to the <br />Divlslon and found to be acceptable. There were problems, however, with retrofitting an open <br />channel spillway on the existing trap. <br />In an effort to avoid construction of a spillway, the Division and Sun discussed the possibility <br />of removing a number of the "lateral" ditches on the reclaimed pit area. We speculated that this <br />would decrease the size of the watershed draining to the trap, and thus elirmnate the need for <br />a secondary spillway. In order to support that assumption, the following demonstrations have <br />been made. <br />1. Gene Shearer, Sun's consulting engineer, studied the existing drainage patterns and <br />produced a sketch of same. Each of the lateral ditches were depicted, and an estimate <br />of the drainage area to each ditch was made. <br />2. Mr. Shearer sent a facsimile of that sketch to the Division, and we discussed with him the <br />resulting watershed sizes if laterals (as labeled on his sketch) "I", "J", "K", "L", and "N", <br />and the trap inlet "M" were removed. Mr. Shearer estimated the drainage area to the <br />Northwest sediment trap, then, would be approximately 20 acres. <br />3. The Division, based on maps and photographs on file, estimates the drainage area (after <br />removal of the above listed ditches) would be 18 acres. <br />4. The Division modeled both an 18 and a 20 acre watershed, using SEDCAD, to determine <br />the resulting runoff and sediment contributions to the trap. The results of that model for <br />a 25-year, 24-hour storm were as follows: <br />20 Acre Watershed: Runoff = .39 acre feet <br />Sediment = .003 acre feet <br />18 Acre Watershed: Runoff = 35 acre feet <br />Sediment = .003 acre feet <br />