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• <br />ty <br />RIVERCITY <br />C O N S U L T A N T S <br />744 HORIZON COURT SUITE 110 970 - 241.4722 <br />GRAND JUNCTION, CO 81506 970 - 2418841 FAX <br />Email: infoOrccwest.com <br />To: Susan Patton, Agapito Associates, Inc. <br />From: Marc Kenney, River City Consultants, Inc. <br />Date: October 20, 2010 <br />Re: Substation Re -Grade Stormwater Calculation Summary <br />The purpose of this letter is to present my analysis of the 10 year 24 hour storm for the <br />catchment draining towards the cut slope of the Substation re- grading area. This analysis <br />included runoff modeling, ditch sizing, and culvert sizing. <br />The catchment of interest is located at the New Elk Coal Mine, owned by New Elk Coal <br />Company, which is a subsidiary of Cline Mining. The New Ells Coal Mine property is <br />located south of Highway 12 approximately 20 miles west of Trinidad, Colorado. The <br />Substation re- grading area and associated upstream catchment are located south of the <br />mine site on the side hill of the ridge running east-west south of the site. North of the <br />• catchment in question is the substation and various mine buildings. South of the site is a <br />diversion ditch, an access road to the site water storage tanks, and the water storage tanks. <br />The area immediately adjacent to the substation is being re -graded to accommodate various <br />minin operations. These operations include rock dust storage, improved substation access, <br />and potential future portal access to various coal seams. The site is located towards the toe <br />of the slope. The hillside above the area to be re -graded is undisturbed except for the <br />diversion ditch and water storage tank access road. The diversion ditch was established to <br />divert runoff from undisturbed catchments around mine operations and disturbed areas. <br />This ditch was established some time ago and appears to be in need of re- design and/ or <br />repair. It is my understanding New Ells Coal Company intends to re- evaluate all diversion <br />ditches and correct any issues in the near future. This analysis assumes this diversion ditch <br />is functioning and can divert 100% of the 10 year 24 hour storm. <br />The vegetative cover for the catchment immediately upstream of the substation re- grading <br />area is pinyon juniper forest in good condition. Soil types are D, and it should be noted <br />bedrock is dose to the surface throughout the area. The hydrologic analysis was done using <br />US EPA SWMM, SCS curve number, Manning's equation, and kinematic wave within <br />Autodesk's Storm and Sanitary Analysis 2011 (formerly BOSS International's StormNET). <br />The model was set up to represent worst case conditions such as back to back storms with <br />saturated soils, or a runoff event occurring with frozen soils. Accordingly, the analysis <br />• s:1PRoiECTs\1134 Agapito - New Elk MineXDesign\StonnNET\Substetion re -grade Calc Summary.doc <br />TR 54 Page E 19(15) -437 Revised 11/2/10 <br />