NorthWestern : Issues February 2017 Update on Hebgen Dam Project; Madison River Basin Snowpack in Good Shape

Butte, Mont. - Feb. 20, 2017 - Work on a spillway replacement project at Hebgen Dam near West Yellowstone is nearing completion and planning is well under way for a project to rehabilitate the dam's outlet pipe, beginning this spring.

In 2009, the Federal Energy Regulatory Commission (FERC) required safety repairs to the Hebgen Dam intake, spillway and outlet pipeline to meet current dam-safety standards and reflect advances in earthquake seismology. The approximately $40 million project is expected to be finished by the end of 2017.

The spillway replacement project is now substantially complete. Removal of the spillway cofferdam is under way and will be complete by early March. The new gates operate under power and the control system will be complete and tested very soon. New security lights and cameras have been installed. Fine grading, topsoil, and seeding of the disturbed areas will be accomplished in the spring along with the replacement of security fencing.

The outlet pipe rehabilitation project at Hebgen is scheduled to begin in the spring. Plans for the project are currently under review by FERC. New permit applications and permit modifications with the appropriate federal and local agencies will be transmitted soon in preparation for the work.

NorthWestern Energy is working to secure a construction contract for the project in the coming weeks. Work on the project will begin as soon as the reservoir elevation and conditions allow. River flows will be diverted to the new spillway during the work, which is expected to be complete in 2017 before winter.

Snowpack for the Madison basin is currently at 100 percent of median. The Natural Resource Conservation Service's (NRCS) Snotel sites above Hebgen are well above average at 115 percent, while the sites below Hebgen are at 89 percent. The NRCS issued an early estimate of the volume runoff forecast for the April to July period on February 3rd which projected Hebgen at 99 percent of normal and Ennis at 91 percent of normal.

The Hebgen reservoir elevation is currently at 6,528.71 feet, which is 6.16 feet from full pool and right at the 10-year average level. January inflows were 83 percent of normal and inflows to date in February are 97 percent of normal. Currently, Hebgen outflow is 870 cubic feet per second (cfs). Expectations are that the flow will stay near this level through the end of the month. However, the daily operation of the Hebgen and Madison hydro projects are subject to constant monitoring, re-evaluation, and collaboration with applicable agencies. Appropriate operational changes will be made, as necessary, taking into account our FERC license requirements.

NorthWestern will work to provide monthly public updates on the schedule and progress of Hebgen outlet-pipe repairs, snowpack and runoff forecasts and related Madison River biological and recreational issues. NWE also proposes public meetings on these same topics in mid-March (Ennis) and in late April or early May (Ennis and West Yellowstone).

About NorthWestern Energy (NYSE: NWE)
NorthWestern Energy provides electricity and natural gas in the Upper Midwest and Northwest, serving approximately 701,000 customers in Montana, South Dakota and Nebraska. More information on NorthWestern Energy is available on the company's website at www.northwesternenergy.com.

Media Contact:
Butch Larcombe
(866) 622-8081
butch.larcombe@northwestern.com