Friday, NOVEMBER 7, 2025 |

Photo – Seminoe Reservoir – Bigfoot99 file photo

County officials raised concerns about the environmental impact of the Seminoe Pumped Storage project.

During the November 4th Board of Carbon County Commissioners meeting, rPlus Hydro Managing Director of Hydro Strategy Matthew Shapiro updated the Board on the proposed pumped storage facility at Seminoe Reservoir.

Shapiro began with an overview of the project, describing pumped storage as a fast, flexible method of balancing the demand on the electrical grid by transferring water between two reservoirs of different elevations.

Managing Director of Hydro Strategy Shapiro said rPlus Hydro is proposing to build a man-made lake on the summit of Bennett Mountain at Seminoe Reservoir. Shapiro said the upper body of water would hold roughly one percent of the total volume of the lower reservoir.

The two bodies of water would be connected via an underground tunnel containing a hydroelectric turbine. According to rPlus Hydro, electricity generated by the facility will travel 29 miles along high-voltage transmission lines to the PacifiCorp-owned Aeolus Substation, located northeast of Medicine Bow.

Managing Director of Hydro Strategy Shapiro explained that Seminoe Reservoir is the ideal site for a pumped storage project.

Shapiro added that the site was identified by the Bureau of Reclamation as one of the most promising locations for a pumped storage facility twice, once in 1963 and again in 2013. The rPlus Director of Hydro Strategy said the Seminoe Pumped Storage project would help meet growing power demands and stabilize the electrical grid as older generation sources are retired.

Should the project be approved, Shapiro said the three-to-four-billion-dollar facility would generate around $9 million in annual property taxes. Additionally, once construction is complete, rPlus Hydro is expected to employ roughly 30 full-time workers.

Shapiro said the only visible elements of the pumped storage facility will be the newly constructed upper reservoir and the transmission lines extending from the site. However, the project is expected to have impacts on tourism and wildlife. Over 900,000 cubic yards of earth must be removed to construct the underground tunnels and powerhouse. The spoilage was originally planned to be dumped at a site nearly four miles from the project location, but Shapiro said rPlus Hydro is considering closer alternatives to reduce the impact of dump truck traffic on local roads.

Perhaps the greatest concern is the project’s potential impact on water quality in Seminoe Reservoir and the downstream ecosystem, particularly the Miracle Mile, a designated blue-ribbon trout fishery. Shapiro said extensive studies have shown that the pumped storage facility will have no measurable impact on water temperatures at the Miracle Mile. However, if temperatures were to fall outside normal parameters, the Hydro Strategy Director said operations would be slowed until conditions returned to normal.

When drawing water from the lower reservoir, Shapiro said studies indicate there will be no adverse impact on the water quality in Seminoe Reservoir. Additionally, mesh screens will prevent fish from being sucked up into the system.

rPlus Hydro is currently undergoing review by the Federal Energy Regulatory Commission, or FERC. Last month, the agency released a 288-page draft report outlining the potential environmental impacts of the Seminoe Pumped Storage project, including effects on soil, water quality, fish, wildlife, and recreation. FERC recommended holding two public comment gathering meetings, one in Rawlins and another in Cheyenne.

Commissioner John Espy asked why the company was not holding a meeting in Casper, noting that most Seminoe Reservoir visitors come from Natrona County. rPlus Hydro Senior Attorney Kevin Baker responded that FERC set the meeting locations. Commissioner Espy expressed his dissatisfaction with Baker’s answer, saying that many Wyoming residents feel that FERC and rPlus are leaving them out of the decision-making process.

Next, Commissioner Espy asked where rPlus Hydro will obtain the water rights to fill the upper reservoir. Attorney Baker said the company was in discussions with the Bureau of Reclamation to secure water rights but had already finalized an agreement with the Casper Alcova Irrigation District. This exchange prompted a meeting attendee to ask how much water it will take to fill the upper lake.

Managing Director of Hydro Strategy Matthew Shapiro said the initial fill would draw 14,000 acre-feet from Seminoe Reservoir, with an additional 400 acre-feet per year to offset evaporation losses.

Four hundred acre-feet equals 130,340,400 gallons of water lost to evaporation from the upper reservoir annually. Commissioner John Johnson was surprised by the amount of loss, saying that much water could be used to irrigate a one square mile plot of land.

Senior Attorney Kevin Baker said rPlus Hydro will pay the Bureau of Reclamation and Casper Alcova Irrigation District for the lost water.

Commissioner Johnson said the system can only be replenished through snow melt. Attorney Baker said the evaporative loss is normal for Seminoe Reservoir and would occur regardless of the fact that the water is being stored in the upper lake, a claim that Commissioner Johnson refuted.

If the Federal Energy Regulatory Commission approves the project, rPlus Hydro will need to secure an interconnection agreement with PacifiCorp to purchase the power generated by the pumped storage facility. Hydro Str