2017-07-11_PERMIT FILE - C1981019A (3)

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RULE 4 PERFORMANCE STANDARDS Sediment will be removed from all sedimentation ponds on an as needed basis or when the sediment level will not allow effective treatment of the runoff resulting from the 10 -year, 24-hour precipitation event in accordance with Rule 4.05.2. Quarterly inspections will note the level of sediment in each pond. Ponds will typically be cleaned of sediment when water levels are lowest, and the least amount of precipitation is expected. The removed sediment may be used as topsoil or subsoil if it meets the suitability criteria discussed under Section 2.04.9 or placed in the backfill of the pits. The Division will be notified of this determination if the material is selected as overburden material that can be substituted for or as a supplement to topsoil. All sedimentation ponds will be designed so that the minimum elevation at the top of the settled embankment is at least one foot above the elevation of the water surface in the pond with the emergency spillway flowing at design depth. Colowyo will design, construct, and maintain the sedimentation ponds to prevent short-circuiting to the extent possible. As a general rule, the inflow to the ponds will be at the opposite end from the outflow area. The constructed height of the sedimentation pond embankment will be designed to allow for settling. During construction, a registered professional engineer will ensure that the appropriate embankment height is accomplished. For all sedimentation ponds, the entire embankment, including the surrounding areas disturbed by construction, will be seeded after the embankment is completed, using the Topsoil Stockpile/Pond Embankment seed mix described below. The active upstream side of the embankment where water will be impounded will be riprapped or otherwise stabilized, where necessary. Areas in which revegetation is not successful or, where rills and gullies develop, will be repaired and revegetated. Colowyo will inspect the condition of each sediment pond, sediment trap, or future post -mining stock reservoir on a quarterly basis. All of these types of structures meet the requirements of an impoundment, and the inspection procedures will meet the requirements under Rule 4.05.9 (17). Previously, Colowyo has received a waiver from quarterly inspections for several existing stock reservoirs within the current permit area as described under Section 4.05.9. This waiver changed the inspection frequency to annual. Following construction of any future post -mining stock reservoir proposed in the Collom permit expansion area, Colowyo may request a similar waiver but until that is approved, the quarterly frequency would apply. Results of all impoundment inspections will be submitted annually. Topsoil Stockpile/Pond Embankment Seed Mix* Western wheatgrass @ 4 Lbs PLS/Acre Thickspike wheatgrass** @ 4 Lbs PLS/Acre Yarrow*** @ 0.15 Lbs PLS/Acre *mix may be modified as a result of an updated Reclamation Plan, currently under review. **option to replace Thickspike wheatgrass with Beardless bluebunch wheatgrass or Sheep fescue ***option to replace Yarrow with Cicer milkvetch 4.05.7 Discharge Structures Please see Section 4.05.7 in Volume 1. The design requirements for sediment ponds for the existing operation can be found in Volumes 2D, 2E, or in Exhibit 7, Item 15, in Volume 13 Design requirements for all sediment ponds associate with the Collom Pit can be found in Exhibit 7, Item 23. Collom — Rule 4, Page 6 Revision Date: 3/3/16 Revision No.: TR -108