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• The road on the west side of Foidel Creek is located in a previously disturbed area, an old road bed, therefore <br />topsoil is not available for salvaging from this azea. The road on the east side of Foidel Creek will be constructed <br />along the toe of Pond C, which is also in a previously disturbed area. On the east side of Foidel Creek limited <br />quantities of topsoil are available for use in final reclamation of the site. The topsoil will be windrowed to the side <br />or placed in a stockpile adjacent to the road. Minor grading will be done in the road con•idor to provide a <br />satisfactory base for subsequent road construction. <br />Safety berms will be constructed on either side of the roadway. The berms will be constructed of spoils materials <br />from the mine site. This spoils material has been used extensively on the mine site in the past as fill material and is <br />not acid-producing. During construction, temporary erosion control measures will be implemented as necessary. <br />Long-term erosion protection will be provided by seeding the out-slopes with an appropriate seed mix and use of <br />selectively placed rock check dams. Mulching, fiber mats, topsoil, or other appropriate medium for the <br />establishment of plant growth may be applied to ensure adequate growth. <br />A structural geo-grid material will be placed above the geo-fabric to distribute loads over the soft soils more <br />uniformly and reduce the required thickness of fill material required which, in turn, reduces the overall footprint of <br />the roadway. Openings in the geo-grid structure are approximately 1 inch by 1 inch. The fill material will lock into <br />these openings and increase the structural stability of the subgrade. <br />Design calculations for the depth of fill required to distribute loading on the road are based on an estimate of the <br />topsoil's shear strength of 5.21 psi in the low areas adjacent to the creek and 10.4 psi in the other areas. <br />Discussions with an engineer with experience constructing roads in this area indicate that typical shear strengths for <br />this type of soil range from 13 psi to 20 psi, so the values used for design calculations are very conservative. North <br />West Colorado Consultants developed a computer model of the road sections and determined factors of safety for <br />deep failure of the subgrade materials in the range of 2.0 and for shallow failures in the range of 1.7 with l:l side- <br />slopes on the embankments. The Tensor design and stability analysis are provided in Exhibit 48. <br />A SEDCAD+ model was performed for the 10-year, 24-hour storm over the contributing drainage basin. The <br />model assumes that the peak flow from Pond A will be occurring concurrent with the ] 0-year, 24-hour event over <br />the basin. A peak flow of 41.86 cfs was determined at the crossing and a minimum pipe diameter of 30" was <br />determined to be adequate to handle the peak flow. Data was reviewed for USGS stream gauging station 09243800 <br />(station 800), located approximately 2,500 feet upstream of the crossing. An instantaneous peak flow of 65 cfs was <br />recorded on May 5, 1996. The recording period for station 800 is 1976 to 1996. An additional culvert run was <br />performed with SEDCAD+ for the instantaneous peak flow of 65 cfs. Headwater depth for this run was based on <br />the design roadway elevation of 6.5 feet above the invert of the culvert. A 36-inch culvert will safely pass the <br />highest recorded instantaneous peak flow with the additional headwater depth provided by the roadway <br />embankment. In order to ensure additional capacity for potential blockage, a 70-foot, 42-inch CMP, or up to a 48 <br />inch CMP, will be installed at the crossing. Slope protection will be provided on both the upstream and <br />downstream sides of the crossing using rock rip-rap. <br />Drainage from the road surface will flow along the ditch line provided by the safety berm. Rock filters or other <br />sediment control measures will be constructed at locations where road drainage flows into the creek as necessary. <br />Drainage from the batch weigh/loadout area is currently directed along the railroad tracks to Foidel Creek. This <br />drainage will continue to be directed between the new road and the railroad tracks. <br />The haulroad will be removed when access is no longer required to the batch weigh/loadout area. Reclamation of <br />the haulroad will consist of removal of the gravel fill material, geo-grid, geo-fabric, and culvert. The gravel fill <br />~trdtz'na~' w~i]' d~ used orr approved pernanenY rtrauk or used ~ r]-i1' marenai' for rPnai graalhg ot~rtl~ digdwai]' an <br />MR 01-174 2.05-72.1 09/26/01 <br />