2025-07-30_PERMIT FILE - C1981019 (7)

Home Browse Search

RULE 4 PERFORMANCE STANDARDS South Taylor – Rule 4, Page 5 Revision Date: 7/21/25 Revision No.: MR-267 under Section 2.04.9. 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. 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 postmining 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 postmining stock reservoir in the South Taylor 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 will be modified as a result of an updated Reclamation Plan submitted after PR-02 approval. Colowyo existing permit Section 4.06.3 must be modified to reference the updated seed mix in this location at that time. **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 can be found in Volumes 2D, 2E, or in Exhibit 7, Item 15, in Volume 13 4.05.8 Acid-forming and Toxic-Forming Spoil Acid forming materials do not exist within the overburden to be removed by the mining operations. A discussion on the overburden at the Colowyo operation has been conducted as set forth in Section 2.04.6. A discussion of the overburden monitoring plan is set forth in Section 2.05. Acid-Base Accounting shows that almost none of the encountered interburden has a net acid-generating potential, and the average acid- neutralizing potential to acid-generating potential ratio ranges from about 50 to about 90 in each borehole in