Laserfiche WebLink
RULE 4 PERFORMANCE STANDARDS <br /> <br />South Taylor – Rule 4, Page 4 Revision Date: 7/21/25 <br /> Revision No.: MR-267 <br /> <br /> <br />Channel lining rock riprap and energy dissipaters will be used when necessary. As stated above, all <br />temporary diversion structures will be seeded and revegetated. Colowyo does not anticipate that there will be <br />any significant excess material resulting from the construction of diversion ditches. <br /> <br />None of the diversions will drain into underground mines. <br /> <br />4.05.6 Sedimentation Ponds <br /> <br />The location, design parameters, and detailed sedimentation calculations of all sedimentation ponds are <br />presented in Erosion and Sediment Control Structures (Exhibit 7, Item 20). The design plans and <br />specifications for the sedimentation ponds are described in this section. All sedimentation ponds will be <br />located as close as practical to the areas to be disturbed. Steep terrain in the upper basins precludes location <br />of the ponds at the disturbance boundaries, necessitating down-valley locations. Other methods of sediment <br />control will be located on the reclaimed areas; these methods include the use of contour furrowing, contour <br />drainage ditches, chisel plowing, and revegetation. <br /> <br />This application contains calculations used to determine runoff volumes and flow rates for the theoretical 10- <br />year, 25-year, and 100-year, 24-hour precipitation events and 50 percent of the probable maximum <br />precipitation (PMP), as well as subsequent sediment volumes. PMP information is required for State <br />Engineer’s Office (SEO) requirements for Class II, small to moderate hazard dams. The precipitation data <br />were obtained from the NOAA Atlas 2, Volume 3 for Colorado; soil types were obtained from the Soil <br />Conservation Service, and are shown on the Soils – South Taylor (Map 5C). <br /> <br />The ongoing mining activities within each watershed of the permit area will create constantly changing <br />hydrologic conditions. The design models are generally based on a static, theoretical scenario, utilizing <br />SEDCAD 4, which considers the worst-case scenario wherein mine phasing has caused impacts to the entire <br />disturbance area and reclamation has not yet been attained for any areas. Refer to Map 12 for a delineation of <br />the areas used for these modeling purposes as well as the individual maps associated with each SEDCAD run. <br />The dates indicated on Map 12 are for development of the worst-case scenario for hydrologic modeling and <br />are not a definitive schedule for mining and reclamation activities. <br /> <br />It is Colowyo’s contention that the models represent nothing more than the best hydrologic estimates for a <br />described worst-case condition. The intent of the modeling is to aid in the design of sedimentation ponds to <br />predict compliance with applicable effluent standards. A primary limitation of the modeling and subsequent <br />designs is the available existing topography, which is very coarse at a 25-ft interval. Colowyo believes it <br />would be an inappropriate use of the SEDCAD models to use them as an enforcement tool for such operations <br />as topsoil stripping; backfilling, grading, reclamation, etc. Furthermore, more detailed topography must be <br />obtained to verify results prior to implementation. <br /> <br />The scenario used for the sedimentation ponds corresponds to an active, disturbed operation. In terms of <br />groundwater, Colowyo’s pits have remained essentially dry. Pumping of pit water (precipitation induced <br />surface runoff) into sedimentation ponds is not anticipated. Discharges from the ponds will remain in <br />compliance with Colowyo’s CDPS Discharge Permit. The use of flocculants in sedimentation ponds may <br />also be used in accordance with the provisions of the CDPS Permit. <br /> <br />Sediment will be removed from all sedimentation ponds on an as needed basis or when the sediment level will <br />not allow effective treatment of the runoff resulting from the 10-year, 24-hour precipitation event in <br />accordance with Rule 4.05.2. Quarterly inspections will note the level of sediment in each pond. Ponds will <br />typically be cleaned of sediment when water levels are lowest, and the least amount of precipitation is <br />expected. The removed sediment will be used as topsoil or subsoil if it meets the suitability criteria discussed