During the construction period, there would be significant activity at the upper reservoir site and along Seminoe Road between the Main Access Tunnel and the spoils site. Activity at the upper site would primarily involve earth-moving activity and concrete-laying and would be heaviest during the non-winter seasons. Activity around the Main Access Tunnel would involve trucks transporting rock out of the tunnel to the spoils area and transporting concrete from the concrete batch plant back into the tunnel. There would also be traffic on Seminoe Road associated with construction crews coming to and from the Main Access Tunnel area, primarily during shift changes.

Minimizing and mitigating construction-related impacts will be subject to rigorous regulatory and licensing review by the FERC and under the NEPA process for the project. An existing road to the upper site, accessed off Kortes Road, will need to be improved for construction access. Any other road improvements needed to minimize dust, etc. will be made per applicable requirements.

It is anticipated that the majority of heavy equipment required for construction at the upper site will be transported in an initial mobilization to the reservoir work area and remain there for the duration of the construction phase. This will help to isolate construction activities to the immediate vicinity of the project and minimize excessive disruptions to the community.

After construction, the project would produce no emissions, noise or light pollution, and traffic would be minimal, limited to required maintenance activities. The upper reservoir dam will not be visible from most public vantage points. The lower intake structure will be near the bottom of the Seminoe Reservoir and will not be visible. Visual simulations of other project facilities were created as part of the preparation of the FERC license application. During project operation, the primary traffic would be during crew changes for staffing the powerhouse, which would be accessed from Seminoe Road. Visits to the upper reservoir site would be minimal.

The project plans to interconnect to PacifiCorp’s transmission system via two new transmission lines transmission line that will run approximately 30 miles to the Aeolus Substation near Medicine Bow. The 500kV line will use lattice towers and is planned to run parallel to two existing transmission lines.

Black Canyon Hydro does not anticipate any impact to most activities on Seminoe Reservoir. It is not anticipated that the project will have any impact on fishing or boating. The potential effects on ice fishing due to small fluctuations in water level are being studied.

The new upper reservoir will be subject to significant daily fluctuations in water levels. For safety reasons in particular, it will not be usable for recreation purposes.

The upper reservoir is located within sage grouse General Habitat Management Areas (GHMA). Most of the proposed transmission line route is located within sage grouse Priority Habitat Management Areas (PHMA). Protection of sage grouse and their habitat is a high priority for Black Canyon Hydro, residents, and state and federal permitting agencies. Field surveys commenced in spring 2021 and will be further undertaken to get an up-to-date and accurate understanding of sage grouse habitat and leks in the vicinity of the project. Any resulting constraints, conditions, or mitigation measures will inform the next steps of project development. Given the relatively small footprint of the project, Black Canyon Hydro believes that the project will be compatible with existing state and federal resource management plan requirements to protect sage grouse and sage grouse habitat in the project vicinity.

The Ferris-Seminoe herd of bighorn sheep occupies areas that include portions of the project site. Portions of the project construction area are within areas designated by Wyoming Game and Fish for minimizing activity, such as traffic, during certain times of the year in order to avoid causing stress to the herd. These are primarily the upper reservoir construction site and the short section of Seminoe Road along which heavy construction vehicles would take material back and forth to the Main Access Tunnel below Seminoe Dam.

Construction activity at the upper reservoir site will naturally slow down during the winter due to minimum temperature requirements for laying concrete, and this slowdown coincides well with winter seasonal sensitivity for the herd. Construction activity along Seminoe Road, which is associated with underground construction for the project, must continue year-round in order for the project to be constructed within an economical timeframe.

In consultation with multiple state and federal agencies, and for the purpose of minimizing the area of disturbance associated with heavy truck traffic, Black Canyon Hydro has proposed changes that would reduce the heavy truck traffic distance to just 1.6 miles—a 60% reduction over the original proposal. This is one of many steps we’re planning in order to minimize and mitigate disturbance to bighorn sheep during the construction of the project. Following construction, traffic activity associated with project operation will be very low.

Rigorous modeling of the project’s potential impact on water temperature and other water quality factors has shown that under typical conditions, the project would not have an adverse impact on the Miracle Mile fishery. Modeling did show that in rare circumstances—a very low water year combined with high air temperatures in the late summer—that full project operation could have a slight effect on downstream water temperature. As part of the permitting process, a project operational plan is being developed in cooperation with the Wyoming Department of Environmental Quality to ensure careful monitoring of temperatures both in Seminoe Reservoir and in the Miracle Mile and to provide for adjustment of project operations, if needed, to protect the fishery.

Potential benefits to water quality, based on the modeling, may include increased dissolved oxygen and lower temperatures within Seminoe Reservoir.

Studies show that the project will have very little impact on turbidity in Seminoe Reservoir and likely no impact on turbidity in the Miracle Mile, which will be monitored. The velocity of water discharged into Seminoe Reservoir will be reduced by the large outlet structure and rapidly drop off with distance from that structure, causing minimal disturbance. Initial start-up of the project is expected to disturb a very small amount of sediment compared with the normal flow of sediment through the system. A rock blanket is proposed to prevent scour throughout operation of the project. Studies were based on up-to-date bathymetry gathered in Seminoe Reservoir in 2021 and sophisticated water flow models based on maximum possible flow rates under both high- and low-water conditions.

Studies indicate minimal risk of impact on fish within Seminoe Reservoir. The primary focus of potential impact there is on entrainment and impingement of fish around the project water intake structure. Risk of entrainment is low due to three factors: (1) the depth of the intake structure is below where fish are generally active; (2) the size of the intake structure is designed to minimize the velocity of water being drawn in, allowing most fish to escape the current; (3) the use of a fish screen on the intake, with gaps small enough to prevent any larger fish from entering.