The Federal Energy Regulatory Commission on Sept. 27 issued for 30 days of public comment an environmental assessment on an October 2015 application from GB Energy Park LLC (GBEP) for a license to construct and operate its proposed Gordon Butte Pumped Storage Project.
The closed-loop, 400-MW project would be located approximately three miles west of the town of Martinsdale in Meagher County, Montana. The project would not occupy federal land.
The project would utilize several existing facilities currently owned and operated by 71 Ranch LP to provide flows or access to the project, but GBEP does not propose to include these features as licensed project facilities. These include: an existing diversion structure on Cottonwood Creek; a 5.5-mile-long, 4-foot-wide, 4-foot-deep earthen irrigation canal; a Parshall flume within the irrigation canal to measure flow diversions from Cottonwood Creek; and a 3.89-mile-long access road.
The Gordon Butte Project would consist of a new upper and lower reservoir, three new dams, a conveyance system between the reservoirs, a powerhouse with generating/pumping facilities, a transmission line and two substations, and an access road to the lower reservoir. The 3,000-foot-long by 1,000-foot-wide upper reservoir would be created by a 90-foot-high, 7,500-foot-long concrete faced rockfill dam built atop Gordon Butte. The upper reservoir would have a normal maximum pool elevation of 6,027 feet mean sea level (msl), an active storage capacity of 4,070 acre-feet, and a surface area of approximately 63 acres. A reinforced concrete combination intake/outlet structure located in the upper reservoir would connect to the powerhouse through a 738-foot-long underground vertical shaft tunnel and a 3,000-foot-long underground concrete and steel-lined penstock tunnel.
A partially buried 338-foot-long, 109-foot-wide, 74-foot-high reinforced concrete and steel powerhouse would be constructed adjacent to the lower reservoir and contain four reversible pump-turbine units rated at 100 MW each for a total of 400 MW. Each turbine would discharge into the lower reservoir through 16-foot-wide, 11.54-foot-high closure gates.
The 2,300-foot-long by 1,900-foot-wide lower reservoir would be created by a combination of excavation and two 60-foot-high, 500- and 750-foot-long concrete faced rockfill dams. The lower reservoir would have a normal maximum pool elevation of 5,057 feet msl, active storage capacity of 4,070 acrefeet, and surface area of approximately 88 acres. The lower reservoir would be located at the northern foot of Gordon Butte.
Water to initially fill the reservoirs (4,685 acre-feet) and to make-up for evaporative losses (approximately 500 acre-feet per year) would be supplied from Cottonwood Creek via 71-Ranch’s existing irrigation system. GBEP proposes to install a trashrack and flow control gate or valve at the terminus of the irrigation canal. The gate or valve would connect to a 150-foot-long, 4-foot-diameter pipe that would carry flows to the lower reservoir.
To access the upper reservoir, GBEP would use 71 Ranch’s existing 3.89-mile-long access road running between Montana Highway 294 and an existing wind farm on Gordon Butte.
Power generated by the project would be transmitted from the powerhouse substation through a new overhead 5.7-mile-long, 230-kV transmission line to a new 1,200-foot-wide, 1,450-foot-long substation, where power would be stepped up to 500-kV, and interconnect with an adjacent existing non-project 500-kV transmission line. The project is estimated to generate 1,300,000 megawatt-hours (MWh) annually.
The Gordon Butte Project would operate as a closed-loop pumped storage system. The project would pump water from the lower reservoir to the upper reservoir at times when energy is in excess or in low demand. When energy is needed, water would be released from the upper reservoir through the power tunnel to the powerhouse to generate electricity. This would occur based on on-peak/off-peak power considerations, the need to augment the production of local renewable wind power generation, or to provide ancillary power services.