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' III DRAINAGE DESIGN CRITERIA <br />' A. Regulations <br />' The runoff for the pre-mining conditions was evaluated using the Sedcad' Version 3 <br />computer program. The hydrologic model was developed by Dr. Richard Warner of the <br />University of Kentucky, who continues to update, extend, represent and support the <br />' program. This program was used over other runoff evaluation models because it has <br />many applications designed specifically for modeling drainage at mine sites. It is <br />accepted by the Bureau of Land Management (BLM), the Office of Surface Mining <br />' (OSM), and the Colorado Division of Minerals and Geology (DMG). Some of these <br />agencies even use Sedcad for cross-checking results from other models for review <br />purposes. Sedcad was developed to assist in the design and evaluation of stormwater, <br />erosion, and sediment control management techniques. It is similaz to the SCS's <br />Technical Release-55 (TR-55) prograzn. Design and evaluation components of the <br />program are highly integrated so that the effectiveness of individual measures as well as <br />1 comprehensive systems of improvements can be readily obtained. <br />Information was provided to County staff upon request prior to use of the model. <br />Permission to use this program was obtained from the Douglas County Public Works <br />Department in the July 6, 1995 pre-application meeting. <br />B. Development Criteria Reference and Constraints <br />1. Previous drainage studies. Tuttle Applegate, Inc. designed a preliminary drainage plan <br />for the DMG Regular Operations (112) mining permit application. This drainage plan <br />proposed to reduce peak discharges and velocities from the outlet points of the mine <br />through the use of excavated sedimentation ponds and a riprap cutoff structure at each <br />outlet point. The plan also proposed to create drainage basins of similar size as the pre- <br />mising basins. <br />The current drainage plan proposes to retain all the stormwater flows within the mining <br />i area. The current approach attains the previous study's objectives of control of peak <br />discharges and sediment. <br />2. Adjacent drainage studies. We aze not aware of any adjacent drainage studies. <br />3. Drainage impacts of site constraints. This operation does not propose to construct or <br />install paved streets, utilities, or permanent buildings, nor w711 drainage impact any <br />existing structures. <br />' Following completion of the mining of the Castle Rock Quarry rhyolite deposit, CMI will <br />have essentially created a mild 10 to 25 foot depression on top of the mesa and drainage <br />in the upland areas will be confined. <br />1 <br /> <br />1 <br />