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• <br />STORM WATER HYDROLOGY <br />Background and Prior Drainage Designs <br />The drainage plan for the mine has previously been designed by others and <br />approved by the Colorado Division of Reclamation, Mining and Safety. The drainage <br />plan for much of the mined area was approved in Amendment No. 8 to Mined Land <br />Reclamation Permit M-1980-244 in 2000. That drainage plan addressed the storm water <br />management of SGOSA and the Valley Leach Facility (VLF) Phase IV. Golder <br />Associates, Inc. subsequently prepared revisions to that drainage plan as were required <br />by extension of the East Cresson Mine in May 2004. These revisions focused on the <br />storm water diversions and ponds in Vindicator Valley drainage basin, EMP011 and <br />EMP012. <br />Methodology and Basin Descriptions <br />The SEDCAD4 computer program was used to model the hydrology because of <br />its ease of use in modeling the system and summarizing results. Attachment B includes <br />summaries of the SEDCAD4 results, the network arrangements and sub-watershed <br />results and additional reports that describe the geometry of the sediment ponds, also <br />known as the Enhanced Management Practice (EMP) structures. <br />Three storm water basins associated with the MLE activities are reconsidered. <br />The watershed storm water basins and the management rationale are described below. <br />• The East Cresson Mine and ECOSA will collect runoff from the most northerly limit of <br />the mine to the east border above Grassy Creek. That area was treated as a basin <br />because the interim EMPs for operations can also be used after closure. <br />• The North Cresson Mine area (Poverty Gulch) storm water basin is the west flank of <br />the mine north of Squaw Gulch. Most of that area, up to the affected land boundary, <br />will be mined as part of the MLEI. Storm water management is necessary during the <br />growth medium salvage and initial development for mining, but the basins will be <br />removed during mining and the drainage will flow back toward the backfilled mine <br />area after reclamation. Therefore, the EMP008b and EMP009 are designed for <br />operation and will not be needed after closure. <br />• Some. revisions to the SGOSA will be necessary for the proposed MLE. The <br />northwest area of the SGOSA will be extended further west than in previous plans to <br />provide additional storage of overburden materials (the .SGOSA Extension). The <br />north and east areas of SGOSA include backfilled mine areas (depressions) rather <br />than overburden impoundments as previously approved. The drainage ditches that <br />previously flowed north to Grassy Creek (per Amendment No. 8) will no longer be <br />Client:CC&V Gold Mining Co. 4/11/08 <br />Title: Storm Water Management, MLE Page 4 <br />