Monday, April 13, 2026 |
Photo – Seminoe Reservoir – Bigfoot99 file photo
Representatives from rPlus Hydro updated the Natrona County Commissioners on the Seminoe Pumped Storage Project.
During the April 7th Board of Natrona County Commissioners meeting in Casper, rPlus Hydro Managing Director of Hydro Strategy Matthew Shapiro and Senior Attorney Kevin Baker delivered a presentation on the proposed Seminoe Pumped Storage facility.
The Utah‑based energy developer rPlus Hydro, which also does business as Black Canyon Hydro, is seeking to build a pumped storage facility at Seminoe Reservoir. Speaking to the Board of Commissioners, Matthew Shapiro explained that the project would include building a new 13,000‑acre‑foot man‑made lake on a nearby mountaintop. During periods of high energy demand, 10,000 acre‑feet, or approximately 3.26 billion gallons, of water would be released from the upper reservoir back into Seminoe. Shapiro said operating the facility would alter Seminoe Reservoir’s water level by one to three percent.
Shapiro said that the proposed pumped storage facility will help stabilize Wyoming’s electrical grid. When energy production is high, water is pumped from Seminoe Reservoir into the upper lake. When demand outpaces production, the water flows back downhill through an underground turbine, generating electricity.
Shapiro said Seminoe Reservoir was chosen because of its existing body of water, meaning rPlus Hydro will only need to build one new lake. He added that the Bureau of Reclamation has identified the area as a suitable site for pumped storage since the 1960s.
Shapiro said most of the facility would be housed underground. Above ground, the project would require construction of a new bridge near Seminoe Dam to reach the underground powerhouse, an intake and outlet structure linking the mountaintop lake with the reservoir, and 29 miles of power lines connecting the site to the Aeolus substation.
Shapiro said the proposed facility can generate up to 970 megawatts of electricity, similar to the Dave Johnson coal‑fired power plant near Glenrock, for 12 hours. With the ability to come online quickly, the managing director of hydro strategy said the project would fit well with the state’s existing energy infrastructure.
Shapiro said most coal‑fired power plants are scheduled to be taken offline by the 2040s, adding that the pumped‑storage project would help meet the state’s growing energy demand, driven in part by large computer datacenters.
Shapiro said the project is expected to cost $2 to $3 billion to build and generate roughly $9 million in annual property taxes, mostly in Carbon County. Construction would create roughly 400 temporary jobs, with up to 35 permanent positions once the facility is completed.
Shapiro added that Natrona County will see an increase in local spending during construction.
Over its six years of development, the scope of the project has changed to address concerns from federal, state, and local stakeholders. Shapiro said the original plan called for mining spoils to be hauled on Seminoe Road to a processing site more than three miles away. The newly proposed location has cut that distance by half.
The Wyoming Game and Fish Department is especially concerned about the project’s impact on the Seminoe-Ferris bighorn sheep herd, which is the last in the state not infected with domestic livestock diseases.
Shapiro said Game and Fish originally placed seasonal restrictions that limited construction to a four‑month window, from May to August, in specific areas to avoid disturbing the bighorn sheep herd. Last year, the agency expanded the herd’s habitat, extending those restrictions to additional parts of the project.
Shapiro said the closer spoils site was chosen in response to the new Game and Fish restrictions.
The majority of concerns about the proposed Seminoe pumped storage project focus on potential impact suspended‑sediment levels and water temperature changes could have on Seminoe Reservoir and the downstream blue‑ribbon Miracle Mile trout fishery. Shapiro said rPlus Hydro spent over two years working with the Wyoming Department of Quality to ensure the project will have no impact on water quality.
After finding no perceivable impact, DEQ issued a Clean Water Act Section 401 Water Quality Certification for the project last month.
As for turbidity, Shapiro said the facility would only stir up the water when initially activated. In addition, the structure that moves water between Seminoe Reservoir and the upper lake will sit on a bed of rocks to keep it from drawing in sediment.
Natrona County Commissioner Dave North questioned how moving 3.26 billion gallons of water between the two reservoirs won’t change the temperature. Shapiro replied that rPlus Hydro and Wyoming DEQ studied the facility’s potential effect on water temperature in depth, down to the degree, and found it would only change during very specific conditions.
rPlus Hydro Senior Attorney Kevin Baker said the temperature threshold was one‑tenth of a degree. Baker said any water‑quality changes would occur only when the facility is operating and added that increased dissolved oxygen may benefit the Miracle Mile trout fishery.
Shapiro said rPlus Hydro will install monitors at Seminoe Reservoir and the Miracle Mile two years before construction begins to establish a baseline water temperature. Once operational, any fluctuations beyond normal levels will require the facility to scale back activity until temperatures return to normal.
Commissioner Dave North asked how much Seminoe Reservoir’s water level would drop while the upper lake was being filled. Managing Director of Hydro Strategy Shapiro said it would fall anywhere from a few inches to more than a foot. Commissioner North then asked the two rPlus Hydro representatives if they had ever boated on the reservoir, and both said they had not. He said lowering the water level could affect recreational users as well as fish.
The rPlus representatives did not respond to Commissioner North’s comments as the discussion moved to evaporative loss. Shapiro said the upper lake is expected to lose 200 acre‑feet, or approximately 65 thousand gallons, a year. However, overall annual evaporative loss for the system is estimated between zero and 80 acre‑feet. Shapiro explained that lowering the water level of Seminoe Reservoir will essentially offset any losses.
Despite the projected net‑zero evaporative loss, Shapiro said rPlus Hydro will still financially reimburse the Bureau of Reclamation and the Casper‑Alcova Irrigation District for 472 acre‑feet per year.
Since the Seminoe Pumped Storage facility is considered a hydroelectric power plant by the federal government, it falls under the authority of the Federal Energy Regulatory Commission, or FERC. Shapiro said in its draft environmental impact statement from last September, FERC concluded that the project’s public benefit outweighs its potential impact on wildlife. The federal agency is expected to issue a final ruling in June, with permitting to be approved in September.
Even with FERC’s approval, Shapiro said rPlus Hydro must still obtain an amendment to the Rawlins Resource Management Plan from the Bureau of Land Management to allow for year‑round construction. In addition, rPlus must also secure a buyer for the electricity. Even once those requirements are met, Shapiro said construction is not expected to begin until 2029 at the earliest.
