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-16- <br />The majority of the culvert works at the site are part of the highway <br />drainage system for Colorado State Highway 13s, and were not reviewed by <br />this Division. All other culverts within the pennit area were reviewed <br />for capacity under conditions of the 10-year, 24-hour storm event peak <br />flow. This was done using procedures detailed in two Federal Highway <br />Administration, U.S. Department of Transportation publications titled; <br />Hydraulic Charts for the Selection of Highway Culverts, 1965, and <br />Hyuraulic Design of Improved Inlets for Culverts. 197 L. All culverts <br />were round to oe aueduateiv size <br />The Norris, East Mine Yard Area, Substation, East Mine Laydown, and West <br />Mine (U.S.S.) ponds were reviewed for compliance with all sections of <br />4.05.6. All ponds reviewed have been found to have satisfactory sediment <br />storage and inflow volume capacities. The only problem identified by the <br />review process is that three of the ponds do not conform to the freeboard <br />requirement of 4.U5.6(8)(d). The rationale for the requirement of 1' of <br />freeboard during passage of the 25-year, 24-hour storm event is to reduce <br />the possibility of embankment destructon during the passage of the <br />25-year, 24-hour storm peak flow. The Division has the policy of <br />allowing variances from the specific design requirements of Rule 4 when <br />it can be shown that no danger to property or life is posed by such <br />variances. Several factors play a role in the approval of these <br />structures, as they exist, without improvement. They are: <br />1) The spillways in question are capable of passing the 25-year, <br />24-hour storm peak flow, <br />~) The spillways in question are constructed of reinforced <br />concrete and as such are not likely to suffer from erosion, and <br />3) Should a failure occur, no injury to life or property is <br />probable. <br />Both the West Mine Pund and the East Mine Laydown Pond meet all the <br />requirements of 4.05.6. <br />Existing disturbances at both the East Portal yard area and the load-out <br />are within 100 feet of the North Fork. The areas were disturbed prior to <br />August 3, 1977 and thus are not subject to the l0U foot stream buffer <br />zone requirement of Rule 4.05.18. Stream buffer zone signs have been <br />installed along the southern perimeter of the disturbed areas at the East <br />Portal yard area and the load-out. H 100 foot stream buffer zone has <br />been established and marked by signs below the West Portal facilities <br />area. IJo furiher surface disturbance will occur within 100 feet of the <br />stream, unless specific variances are granted by the Division. <br />The proposed operation is in compliance with the requirements of this <br />section. <br />