2012-02-28_REVISION - M1980244 (65)

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Cripple Creek & Victor Gold Mining Company Squaw Gulch Valley Leach Facility Design These curve numbers were used to develop a single composite curve number for each sub watershed based on areas of land use and soil types. Reclaimed overburden facilities and the reclaimed VLF were assigned a curve number of 71. 6.3 Diversion Analysis and Design The stormwater diversion channels for the VLF referenced in this design package are shown on Drawings A500 through A507 for Phase 1, and Drawings A510 through A530 for Phase 2, with sections and details on Drawing A550. The diversion structures are primarily trapezoidal diversion channels that are located around the perimeter of the VLF. Roadside diversion channels are also included in areas with low peak flows and /or small watersheds. In addition, where needed, diversion channels along roadsides and elsewhere will collect storm water flows and direct runoff to the trapezoidal diversion channels. Operational trapezoidal and roadside diversion channels were sized to convey the 100 - year /24 -hour peak flows. In some areas, corrugated steel pipes (CSPs) are proposed to convey runoff down steep slopes or under roads. Channel and pipe sizing were performed using Manning's equation in a spreadsheet with uniform flow and normal depth. Riprap for erosion protection was included on channels where the design peak velocities exceeded 5 feet per second. Riprap for rock chutes was sized using rock chute design methodology (Robinson et al. 1997) and channel riprap was sized using the Federal Highways Administration (FHWA) tractive force analysis method. Channel sizes are presented in Table 6. As noted previously, the VLF is planned to be constructed in two phases. During staged construction, temporary diversions will be constructed to route surface water around the VLF until the ultimate VLF footprint and diversions are constructed. Approximate surface water diversion channel sizing and directions of temporary surface water routing are also shown on Drawing A500 and summarized in Appendix F.2. The engineering designs contained in this document are based on the best information currently available and provide a detailed description of the project features associated with the VLF. Because construction will be implemented over many years, it is anticipated that additional information may need to be submitted to the OMLR prior to construction of certain project components. In those instances where the submittal of further information is warranted, CC &V will provide IFC drawings and appropriate supporting documentation (e.g., calculations, narrative explanations, etc.) to the OMLR containing design details and changes that are based on site - specific conditions and constraints. Comparable to previous permitting and approval activities, submittal of the IFC drawings and any supporting information is not expected to require new approvals but is intended solely to ensure that the OMLR is aware of the phased implementation of the construction activities. It is recognized that certain design Project No.: 74201125G0 Page 34 1 September 2011 amec'3