Developers outline 970 MW Seminoe pumped-storage project; county hears timeline, water-quality safeguards and economic claims

Developers from R Plus presented a detailed overview April 7 of a proposed pumped-storage project at Seminoe Reservoir that they said would deliver about 970 megawatts of dispatchable power and up to 12 hours of energy storage.

Matthew Shapiro, managing director of hydro strategy for R Plus, and Kevin Baker, the project’s senior attorney, described a largely underground design with a new upper reservoir (about 120 acres) and an active storage volume of roughly 10,000 acre‑feet. They said the project would require a 29‑mile transmission line to PacifiCorp’s Aeolus substation and estimated an up-front development cost in the range of $3 billion–$4 billion, 300–500 construction jobs and 30–35 permanent positions if built.

Permitting and environmental review figures prominently in the schedule the developers presented. They said the Federal Energy Regulatory Commission (FERC) is the lead federal agency for licensing and that a final environmental impact statement was expected in June with a possible FERC record of decision and license in September under the current schedule. The developers also noted that substantial additional engineering and FERC dam‑safety review work could delay the start of construction until at least 2029, and that a long‑term power purchase agreement must be secured for the project to proceed.

Water‑quality and fisheries concerns dominated commissioner questions. The presenters described two-and-a-half years of modeling with Wyoming DEQ focused on temperature, turbidity and fish entrainment risks, and they said DEQ issued a 401 water‑quality certification based on an adaptive‑management plan that includes continuous monitoring and the regulatory authority to curtail project operations during certain high‑risk conditions. Kevin Baker said the worst‑case modeled exceedance risk to the tier‑one temperature standard was about 0.1° under rare, late‑summer low‑water conditions and that the DEQ conditions include two years of pre‑operation baseline monitoring.

Developers said estimated direct evaporation from the new upper reservoir would be a bit over 200 acre‑feet annually but that net project evaporation (accounting for minor changes to Seminoe’s surface area) would be about 0–80 acre‑feet per year; they also stated they would contractually assume an obligation (cited in the presentation as ~472 acre‑feet) as part of water agreements. The team said they are coordinating with USBR, the state engineer, and the Casper Alcova Irrigation District on water‑rights and contractual matters.

Commissioners and attendees asked about recreational safety (boat hazards from daily drawdown), construction impacts to bighorn sheep habitat, workforce housing, and traffic on Seminole Road; developers described alternatives to reduce haul distances, seasonal constraints to avoid disturbance, and additional mitigation measures under negotiation with Wyoming Game and Fish, BLM and USBR.

The presentation closed with a reminder that the project is still marketing for a power‑purchase agreement and that significant steps remain before construction could begin. The developers offered to receive additional questions from community members and agencies.