The Public Service Commission of Wisconsin on May 7 posted to its website a final environmental assessment on Wisconsin Electric Power’s (WEPCO) plan to rebuild its Twin Falls hydroelectric facility.
WEPCO has requested approval from the commission for work at the existing Twin Falls dam site on the Menominee River, near Iron Mountain in Dickinson and Iron counties, Mich., and near Florence in Florence County, Wisc. WEPCO proposes to replace the existing Twin Falls powerhouse, located on the Michigan side of the river, with a new powerhouse located on the Wisconsin side of the river.
New turbine generators would be installed in the new powerhouse, increasing the installed capacity from 6.1 MW to approximately 9.0 MW, and a new 720-foot electric tie line would cross the river to connect the generators to the existing substation. Additional spillways would be constructed to provide spillway capacity sufficient to pass floodwater at this site.
This new tie line would include three sets of three poles approximately 70 to 80 feet in height, one set on the Wisconsin side of the Menominee River and two sets on the Michigan side of the river, and would cross the Menominee River north of the current American Transmission Co. LLC (ATC) electric transmission line crossing.
Additional spillways are needed in order to provide spillway capacity sufficient to pass the project’s inflow design flood for this site. The existing powerhouse and all associated generating equipment would be removed, and the current forebay would be drained and its entrance closed using a closure dam. The existing powerhouse site would be restored to a natural condition.
The dam would continue to be operated as a modified peaking facility within the flow release constraints described in the Wilderness Shores Settlement Agreement (WSSA) and the existing Federal Energy Regulatory Commission license conditions. WEPCO is not proposing any change to the operation described in the FERC license and the WSSA. The increased hydraulic capacity would allow electric generation using flows greater than the current maximum flow of 2,530 cubic feet per second (cfs)—up to 2,900 cfs. Currently, flows in this range are spilled.