The U.S. Bureau of Reclamation, with the Western Area Power Administration as a cooperating agency, has issued a draft environmental assessment (EA) on a proposal to develop a 9.4-MW hydroelectric project at the existing Helena Valley Pumping Plant site at Canyon Ferry Dam on the Missouri River near Helena, Montana.
The new hydropower generator would interconnect to Western’s transmission system at an existing transmission line originating at Canyon Ferry Dam. Comments on the draft EA are being taken until Nov. 13, with an Oct. 22 public meeting on it planned in Helena.
The Helena Valley Irrigation District (HVID) has requested approval to develop hydropower from the Bureau of Reclamation with respect to this hydroelectric project. Reclamation would execute a Lease of Power Privilege (LOPP) with HVID. In order to acquire the necessary experience in developing, financing, designing, and constructing hydroelectric facilities similar to the proposed project, HVID has entered into a binding Memorandum of Understanding, and subsequently a project development agreement (altogether referred to as the MOU) with Sleeping Giant Power LLC (SGP).
The LOPP would authorize the use of federal lands, facilities, and water to construct, operate, and maintain a 9.4-MW facility. Reclamation and the Western Area Power Administration would also issue appropriate agreements to allow the construction, operation, and maintenance of between 0.27 to 0.34 miles of overhead 12.5-kV three-phase distribution lines to connect the new facility to the existing electrical grid.
The project would be located in Lewis and Clark County, Montana, approximately 10.0 miles southeast of the town of Helena, Montana. It is to to be located at the site of the Pumping Plant adjacent to the Canyon Ferry Dam/Reservoir and related infrastructure on the Missouri River near Helena. The project would include:
- a retrofit of the Pumping Plant’s existing mechanical water pumping equipment and the addition of new electrical generators and other related equipment;
- enclosure of the existing structure above the Pumping Plant;
- electric generation using the existing water required to operate the Pumping Plant for irrigation purposes as well as a portion of the seasonal runoff water that would have flowed through the Canyon Ferry Dam river outlet gates and over the spillway, when available; and
- overhead distribution line alternatives and right-of-way (ROW) options from the hydropower plant to interconnect with existing Western Area Power Administration transmission lines via a new 12.5 kV to 100 kV substation to be constructed on federal property.
A purchase power agreement has been executed to sell the power to NorthWestern Energy, said the draft EA.
HVID was built from 1956 through 1958 and was designed to reclaim land inundated by the backing up of water from Canyon Ferry Dam. The HVID Pumping Plant consists of a three-story enclosed pumping plant located approximately 500 feet downstream of Canyon Ferry Dam.
This project would utilize the power generated from the existing turbine runner in the Pumping Plant. A generator would be directly coupled to the existing turbine shaft. The turbine is currently directly coupled to the pump impellor. This shaft would be extended above the pump impellor allowing the connection to the new electrical generator. The generator would be able to operate over a range of speeds and match the desired speed of the pumps.
Two 4.7-MW, variable speed generators would be installed, one on each existing mechanical pump. The generators would produce electricity at 690 Volts and use inverters and a step up transformer at the powerhouse. Electricity would be transmitted at 12.47 kV to the proposed substation where a transformer would step up the voltage to 100 kV, allowing interconnection with Western’s transmission line. The required pumping flowrate would be dictated by HVID. This pumping flowrate command would control the speed of the generator by adjusting the wicket gates and thus, the generator output.