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~~ CIVIL RES-AU RCES, LLC May 6, 2005 ~~~~"rz`~?G . MAT i Q 2005 Colorado Department of Transportation pivisian of P.;;:;cz_.. °: rs ~:ir Mr. Joe Intermill 43379 Highway 51 Ault, CO 80610 RE: SW TKO Joint Venture, LLC, Division of Minerals and Geology Application M•2004-079' Lupton Lakes Resource; CDOT Objection Letter - Dewatering Dear Mr. Intermill: This letter is being written to present new and confirm previously presented information regarding your concern with respect to passage of water through the Highway 65 right-of-way. Following is the excerpt from your letter regarding the use of the existing structures to convey water to the South Platte River and a brief chronology of communications with CDOT staff and consultants: CDOT Comment 1: Please clarify the points of discharge for wafer that is dewatered to facilitate mining and reclamation plan. CDOT is concerned if the structures under Highway 85 are adequate to handle the flows from pit dewatering. Please demonstrate that the outlet structures (such as ditches, culverts, pipes, etc.) are adequate to handle the flaws from water discharged off-site. Applicant Response 1: The total conveyance capacity requirement at each seepage ditch crossing was estimated by the applicant by adding the 100-year peak runoff rate to the maximum mine dewatering discharge rate. The applicant completed hydrologic calculations to estimate 100.year peak storm runoff discharge rates that would be tributary to each proposed discharge site. The Ogilvie Seepage Ditch crossing peak discharge was calculated to be approximately 78 cfs with a time of concentration of 27 minutes and basin area of approximately 180 acres. The peak storm runoff rate to the Porter Seepage Ditch crossing was estimated to be slightly higher at 87 cfs due to a slightly larger tributary basin area of 200 acres. The applicant proposes to add 45 cfs (and more typically 10 cfs) to this flow for 123 cfs and 132 cfs at the Ogilvie or Porter Seepage ditches respectively. The hydraulic capacity of the conveyance structures at both discharge locations was subsequently calculated. Two culverts exist at each proposed dewatering discharge site. The proposed discharge points are shown on Figure 1. The south discharge location (Porter Seepage Ditch, see Photos 1 and 2) has an 8-foot high by 8-foot wide concrete box culvert and a 24-inch diameter reinforced concrete pipe. The approximate capacity of the 24-inch culvert is 30 cfs and the box culvert capacity is approximately 500 cfs for a total of 530 cfs. (~ -~~c ~1