Complete Application Received - North Twin Project, Maine

May 28, 2021: The Low Impact Hydropower Institute has received a complete application for Low Impact Certification of the North Twin Hydroelectric Project. LIHI is seeking public comment on this application. Specifically, we are interested in knowing whether you think the Project meets the LIHI Low Impact Certification Criteria, as revised in the 2nd Edition Handbook. Please review the program and criteria in LIHI’s revised Handbook and then review the Project’s application materials below.

Comments that are directly tied to specific LIHI criteria (flows, water quality, fish passage, etc.) will be most helpful, but all comments will be considered. Comments may be submitted to the Institute by e-mail at with “North Twin Project Comments” in the subject line, or by mail addressed to the Low Impact Hydropower Institute, 1167 Massachusetts Avenue, Arlington, MA 02476. Comments must be received on or before 5 pm Eastern time on July 27, 2021 to be considered. All comments will be posted to the web site and the applicant will have an opportunity to respond. Any response will also be posted.

The Penobscot Mills Project (FERC No. 2458) consists of four hydroelectric developments and a storage dam located in the general vicinity of Millinocket/East Millinocket, Maine located between river miles 2 and 15 on the West Branch of the Penobscot River. The four developments, listed in order from upstream to downstream, are: North Twin, Millinocket, Dolby, and East Millinocket. The Project developments were originally constructed beginning around the turn of the 20th century to meet the hydromechanical and hydroelectric demands of the Millinocket Mill, constructed in 1900, and the East Millinocket Mill, constructed in 1906. The Millinocket Lake Storage Development contains a pumping station, located on the opposite end of the lake from the Millinocket Lake Dam, that allows water to be pumped up 12 ft from Millinocket Lake to Ambajejus Lake (part of the North Twin impoundment).

The North Twin Development is located in Penobscot and Piscataquis Counties to the west of Millinocket, Maine, and North Twin Dam is positioned approximately 14.9 river miles above the confluence of the East and West Branches of the Penobscot River. The North Twin Dam and powerhouse are located approximately 2.6 miles upstream of the Quakish Lake (a.k.a. Stone) Dam, and approximately 33.4 miles downstream of GLHA’s Ripogenus Dam (FERC No. 2572).

The Project consists of : 1) an impoundment having a normal high water surface elevation of 491.92 ft; 2) a concrete and earth-filled dam measuring approximately 1,051 ft in length, including an intake structure and powerhouse containing three generating units and appurtenant equipment; 3) a series of six earthen dikes having a combined length of 2,530 ft, located upstream of the dam; 4) a 60 Hz substation containing six transformers; and 5) a transmission line approximately 4.2 miles in length that extends to GLHA’s Millinocket substation.

The North Twin Dam is a concrete and earth-filled structure located at the outlet of the North Twin impoundment. The powerhouse and concrete sections of the dam are located between the earthen dike sections; a 500 ft long southern dike and a 286 ft long northern dike. The dam also consists of a 114-ft-wide intake structure and powerhouse and a 117-ft-long Tainter gate section. A 34-foot- wide concrete section, containing a pool and weir design fishway and two gated log sluice sections, is located on the opposite end of the powerhouse from the southern earthen dike. Three gates located upstream of the fishway control the flow of water into the chambers of the fishway. Each of the gates measures 1 ft 3 in. wide by 2 ft high. The gates are located at different depths so the fishway can remain operable at various impoundment elevations. The chambers of the fishway extend downstream of the gate approximately 98 ft along the northeastern side of the powerhouse. A series of five auxiliary dikes, having a combined length of approximately 1,850 ft, are located along the eastern shore of the impoundment near the dam. All of the dikes have a crest elevation of between 497.6 ft and 498.1 ft and a minimum top width of 10 ft. The dikes are of common earth fill construction with sheet pile located within the fill. A sixth auxiliary earthen dike, measuring approximately 680 ft in length, is located approximately 11 river miles upstream of the dam in the area located between the North Twin impoundment (at Ambajejus Lake) and Millinocket Lake.

Project Name North Twin
LIHI Certificate No. N/A
LIHI Certificate Term N/A
Owner Great Lakes Hydro America, LLC - A subsidiary of Brookfield Renewable Energy Group
State Maine
Location River Mile 14.9 of the West Branch of the Penobscot River (as measured from the confluence of the East and West Branches of the Penobscot River)
Installed Capacity 9.84 MW
Average Annual Generation 51,541 MWh
Facility Type Storage
FERC No. 2548, issued 1996, expiring September 30, 2026