Laserfiche WebLink
~..v~ <br />' ~ _ ~ CIVIL RES'S.URCES,.LLC. <br />May 6, 2005 <br />Colorado Department of Transportation .. <br />Mr. Joe Intermilf <br />43379 Highway 51 „ <br />Ault, CO 8061U „ <br />RE: SW TKO Joint Venture; LLG, Division of Minerals arfd Geology Applicatio`ri;M-2004079 <br />Lupton Lakes Resource; CDOT Objection Letter - Dewatering <br />DearMr. lntennili: <br />This letter is being written to present new. and confirm previously presented information regarding your <br />concern with respect to passage of water through the Highway 85 right-of-way. Following is the excerpt <br />from ydur letter regarding the use of.the existing structures to convey water td the South Platte River and a <br />brief chronology of communications with CDOT staff and consultants: <br />CDOT Comment 1: <br />Please clarify the pdints of discharge for water that is ifewateted to facilitate mining and reclamation plan. <br />CDOT is concerned if fhe structures under Highway 85 are adequate to handle ftie-flows from pif <br />dewatenng. Please demonsfrafe fhat fhe outlet structures (such as dtches, culverts, pipes, efc.}are <br />adequate to handle the flows from water discharged off-site. <br />Applicant Response 1: <br />The total conveyance capacity requirement at each seepage ditch crossing was estimated by the applicant <br />by adding the 100-year peak runoff rate to the maximum mine dewatering discharge rate. The applicant <br />completed hydrologic calculations to estimate.100-year..peak.storm runoff discharge rates that would be . <br />tributary to each proposed discharge site.. The Ogilvie Seepage pitch crossing peak discharge was <br />calculated to be approximately 78 cfs with a time of concentra8on of 27 minutes and basin area of <br />approximately 180 acres. The peak storm runoff rate to the Porter.Seepage Ditch crossing was estimated <br />to be slightly higher at 87 cfs due to a slightly larger tributary basin area of 200 acres: The applicant <br />proposes to add 45 cfs (and more typically 10 cfs) to this flow for 123 cfs and 132 cfs at the Ogilvie or Porter <br />Seepage ditches respectively. . , _ <br />The hydraulic capacity of the conveyance structures at both discharge locations was subsequently, <br />~alcufated. Two culverts exist st each proposed dewatenng discharge site. The proposed discharge points <br />are shown on Figure 1. The south discharcje location (Porter Seepage Ditch, see Photos 1 and 2) has an <br />8•foot high by 8-foot wide concrete lax culvert and a 24-inch diameter reinforced concrete pipe. The. <br />approximate capacity of the 24-inch culvert is 3D cfs and the box culvert capacity is approximately 500 cfs <br />for a total of 530 cfs. _ <br />I <br />