2013-02-27_REPORT - C1981028 (7)

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AHR -2012 -74- SURFACE WATER HYDROLOGY The site drainage plan and descriptions of associated structures for the CEC Keenesburg Mine site are found in Appendix K of the Permit. Historically, as part of the reclamation process, CEC continues to maintain the diversion ditches, drainage ditches and drainage swales along the roads and around the north and east sides of the Permit Area. These features serve to convey all surface water runoff to Sediment Pond 2. The present drainage facilities, as well as existing site topographic features, are identified on the Existing Surface Features and Utilities Map (see page 122). Certain surface water control features have been designated permanent facilities (by Permit revision, and at the direction of CDRMS and others). These features will remain following the completion of all site reclamation activities. The permanent features include: • Sediment Pond #2, • The East and the West Perimeter Ditches • The Dugout Pond These permanent drainage features are identified on the Reclamation Contour and Drainage Plan Map (see page 123). With the exception of Sediment Pond 2 and the Dugout Pond, all previously existing man -made temporary pond sites have been closed, and deleted from the drainage control mapping and monitoring requirement. This action was deemed appropriate because: 1) the sedimentation infill of Sediment Pond 2 has been virtually non - existent after more than fifteen years of continuous use; 2) Sediment Pond 2 has not had significant amounts of water stored in it for more than brief periods (except during the unusual and prolonged periods of excess precipitation in 1995 and 1999), and 3) even considering those unusual events of 1995 and 1999, to date there has not been an observed discharge from Sediment Pond 2. Further, CEC implemented a dewatering scheme for Sediment Pond 2 in 1997, in conjunction with the preparation of a, "Spill Prevention, Control and Countermeasures Plan" for the site. This plan was last updated in 2012, and is the subject of annual review. According to the plan, and when conditions warrant, CEC personnel will pump excess runoff water accumulated in Sediment Pond 2 back to the Dugout Pond, located about 700 feet slightly upgradient and to the south - southeast on the CEC property. The Dugout Pond has an available storage capacity exceeding the total contributing runoff volume associated with a 100 -year, 24 -hour design storm event (Technical Revision, "Drainage Control Plan II ",