All Things Colstrip



The Colstrip Steam Electric Station consists of four generating facilities. Units 1 and 2 are 307 Megawatts each and Units 3 and 4 are 740 Megawatts each (Nameplate capacity is cited and is larger than actual generation of delivered electricity).

Construction of Units 1 and 2 began in 1972 and they came online in the mid 1970s. Unit 3 came online in 1983 and Unit 4 in 1985. All four units were certified by the Montana Board of Health and Environmental Sciences. The functions of the Board of Health and Environmental Sciences are now carried out by DEQ. Agreement to Comply Certificate for Units 3 and 4 Units 1 and 2 ceased operation and essentially closed in early January of 2020. More information on the closure is available through the Legislative Services Division.

The modern town of Colstrip in Rosebud County was established during the construction phases of the plants and remains as a community of workers and support businesses for the electric generation facilities. The town draws drinking water from the Yellowstone River by a system that also supplies the generation facilities.

The six utilities with ownership in the generation plant paid the town of Colstrip and Rosebud County more than $13 million in 2014 in the form of property taxes. The coal mine paid nearly $9 million in county taxes that year.

The plants are partially owned by Talen Energy of Pennsylvania, which is also the operator of the facility. Riverstone Holdings, a New York City-based investment company, completed its acquisition of Talen in December 2016. Coal for the facilities is mined from the nearby Rosebud Mine, which is owned by Western Energy company, a subsidiary of Westmoreland Coal of Colorado. The mine is permitted by the federal Office of Surface Mining or through the state by DEQ. Other partial owners of the generation plant include Puget Sound Energy, PacifiCorp, Portland General Electric, Avista, and NorthWestern Energy.

Regular operation of the generation facilities produces coal ash, which has historically been placed in ponds surrounding the plants. Some are used exclusively by Units 3 and 4 while others are used by all four units. By the 1990s, monitoring wells indicated significant leakage of the ponds into groundwater. DEQ and Talen Energy have an Administrative Order on Consent to address this seepage of toxic elements into groundwater. The 2016 Annual Plan and a Five-Year Plan for the AOC are on-file. View PDF

The Colstrip plants are also permitted by DEQ's Air Programs. Restrictions include visible emissions that affect opacity, particulate matter, and Sulfur Dioxide and Nitrous Oxide levels. The current permit also requires Talen Energy to install scrubbers and provide a plan to meet restrictions. View PDF

DEQ also permits the Rosebud Power Plant, also known as Colstrip Energy Limited Partnership (CELP), a small electric generating facility six miles north of Colstrip. Air Quality Permit


Colstrip at a Glance

TOTAL GENERATING CAPACITY = 2094 MW (reduced by roughly 614 MW through closure of Units 1 and 2: 1480 MW)

PSE owns 32 percent of the plants' generation with half ownership in Units 1 & 2 and 25 percent of Units 3 & 4.

PGE owns about 14 percent of the plants' generation, 20 percent of both Units 3 & 4.

PacifiCorp, which does business in Oregon, Washington, and Idaho as Pacific Power and Rocky Mountain Power, owns about 7 percent of the plants' generation, 10 percent of both 3 & 4.

Avista, Spokane-based utility serving eastern Washington, Northern Idaho, and Juneau, Alaska, owns about 7 percent of the Colstrip generation, 15 percent of both Units 3 & 4. Avista was recently under a purchase agreement by Hydro One of Toronto, Canada. That agreement was turned down by the Washington State Utilities and Transportation Commission in December 2018.

The Montana regulated utility based in South Dakota owns 30 percent of Colstrip Unit 4.

The company that operates Colstrip sells electricity to wholesale and industrial customers and electric cooperatives. It owns one-half of Units 1 & 2 and 30 percent of Unit 3. Talen has no ownership in Unit 4.


This small electric generation plant was originally certified by the Federal Energy Regulatory Commission (FERC) as a Qualifying Facility in 1984 under provisions that address use of waste fossil fuels. The plant was authorized to burn “waste coal” (subbituminous) from then-Western Energy’s Decker mine. FERC had determined certain coal from the Rosebud Mine to be “waste” material.

  • Status: Qualifying Facility (QF), 1984; 1998; recertified 2006. (Federal Energy Regulatory Commission and Montana Public Service Commission)
  • Ownership: Owned and operated by Colstrip Energy Limited Partnership (CELP), Boise.
  • Location: Six miles out of Colstrip.
  • Staff: Employs 25 people.
  • Fuel: Waste coal, principally from the Rosebud Mine, Decker.

CELP Permit Downloads

Click a button to download permit

Title V Operating Permit

Air Quality Permit




  • Colstrip Units 1 and 2 cease operation in early January of 2020 and are essentially closed.
  • NorthWestern Energy issues a Press Release in early December of 2019 expressing a desire to purchase for one dollar a 25 percent share of Colstrip Unit 4, along with additional capacity on the transmission line, from Puget Sound Energy.
  • In November 2019, Avista Corp. announces that it will accelerate its exit plans for Units 3 and 4 by 2025 as part of a settlement agreement with intervening parties in Washington State. Puget Sound Energy and PacifiCorp also face Washington state's "coal-free-by-2025" deadline. A group of environmental organizations filed in federal court in Billings in mid-November to challenge the Office of Surface Mining Reclamation and Enforcement approved expansion of the Rosebud Mine, known as Area F. In March and April 2019, NorthWestern Energy issues a plan before the Legislature to purchase a larger share of Colstrip (up to 150 Megawatts) and to carry $40 million to the ratebase over a five year period. The bill (SB 331) fails as both parties and environmental groups question financial aspects of the measure.
  • In November 2018, Montana DEQ and the Office of Surface Mining Reclamation and Enforcement (OSMRE) issue a joint Final Environmental Impact Statement for Western Energy Company's expansion, known as Area F at the Rosebud Mine (see Coal Mining). Westmoreland Coal, owner and operator of the Rosebud Mine, files for bankruptcy in early December 2018. In March 2018, Hydro One, Ltd., of Toronto, Canada and Avista Corp., of Spokane, agree to merge for $5.3 billion; the plan is initially accepted by the Washington State Utilities and Transporation Commission and the Public Servcice Commissions of Montana and Alaska. In August 2017, Talen Energy reverses an earlier decision and announces it will operate the Colstrip facilities into the forseeable future. In November 2018, the Washington Utilities and Transportation Commission cites “careless disregard” by the province of Ontario, the major stockholder of Hydro One, and effectively halts the proposed merge/purchase of Avista. Talen Energy (Riverstone Holdings) and PPL Corporation file countering lawsuits regarding the terms of the 2016 sale.


  • Earth Justice and Talen Energy sign a settlement on converting to a “non-liquid” or dry stack disposal system for coal combustion residuals no later than July 1 2022. This only applies to the Units 3 & 4 ponds. DEQ signs on the settlement to provide approval because of the Administrative Order on Consent the agency is administering.
  • A separate settlement between MEIC/Sierra Club and the Colstrip Partners calls for Units 1 & 2 to close by the year 2022.
  • Riverstone Holdings completes merger with Talen Energy.
  • See also: 


  • PPL Corporation announces it is spinning off subsidiary assets in Montana and elsewhere to newly-formed Talen Energy, also of Pennsylvania.
  • The Environmental Protection Agency issues its Coal Combustion Residual Rule, which regulates coal ash as a non-hazardous waste, calls for numerous requirements for ash ponds, and calls for industry self-implementation.


  • Colstrip Unit 4, offline for scheduled maintenance during May and June, fails upon return to service and remains down for four months.


  • PPL Corporation settles with the Montana Department of Environmental Quality over leaking coal ash ponds, requiring the company to clean up the problem. An Administrative Order on Consent is signed and filed (Colstrip AOC Final Official Record). The settlement is challenged in court by the Sierra Club, the Montana Environmental Information Center, and the National Wildlife Federation.


  • The census lists 2,214 people living in 863 households in Colstrip.


  • Colstrip power plant owners settle with residents of the town over contaminated groundwater linked to leaking ash ponds. The settlement is $25 million and the town of Colstrip becomes fully reliant upon water piped 30 miles from the Yellowstone River and contained in Castle Rock Reservoir.


  • NorthWestern Energy emerges from Chapter 11 bankruptcy.


  • Colstrip power plant owners are sued by 57 residents of the town over contaminated groundwater linked to leaking ash ponds. Boron, sulfate, chloride, and other contaminants are identified.
  • The Montana Legislature exempts coal-fired power plants from the Major Facility Siting Act, essentially eliminating coal combustion wastes such as ash from state regulation.
  • NorthWestern Energy files for Chapter 11 bankruptcy, listing $2.2 billion debt.


  • Montana Power Company sells its shares in Colstrip Unit 4, and associated contracts, and leases to NorthWestern Energy.


Colstrip Map

View the map of the Colstrip area.

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Google Time Machine Imagery

NOTE: Under the Start/Stop tab that shows the year is a setting from Fast to Slow. The slow setting works best. At the bottom, the Peabody Big Sky Mine and the WRI Rosebud Mines are in the immediate Colstrip area. The Big Sky Mine has not produced since 2003 and is in the latter stages of reclamation.

View Google Time Machine - Western Energy

View Google Time Machine - Big Sky Mine


The Energy Bureau compiles and maintains energy production and consumption statistics for the Legislature’s Environmental Quality Council. Texts of the reports may be found in the publication, Understanding Energy in Montana.

Energy Bureau's Site for Energy Statistics

NOTE: Click on Electricity and/or Coal Tables Workbook

Coal Mining

The Rosebud Mine (Western Energy Company, a subsidiary of Westmoreland Coal) is the only mine in active operation at Colstrip. DEQ is involved in the permitting of five separate areas (Areas A through E) comprising roughly 25,000 acres. Visit this StoryMap of Mining & Reclamation for Permitted Coal Mines and navigate to Western Energy Company. Western Energy Area F has a pending permit with DEQ and appropriate federal agencies for roughly 7,000 acres. The Final Environmental Impact Statement for Area F was issued in November, 2018. The Cover Letter and Final EIS are now available. A Montana Pollution Discharge Elimination System (MPDES) permit for the Rosebud Mine (MT0023965) can be found under the tab for Water. Bonding for the Rosebud Mine is at $145 million. Peabody Coal Company's Big Sky Mines are in closure with some remaining permitting through DEQ.

Topic Download
Western Energy Response to Deficiency Letter
Area F August 29, 2016
Response to Deficiency Letter
Area F, February 29, 2016
Environmental Assessment for Expansion of Rosebud Mine
Area B, December 3, 2015
DEQ Findings for Additional 49 Acres, Rosebud Mine
Area B, December 4, 2015
Coal Program's Pending Applications

Coal Ash

In 2012, DEQ took an enforcement action by entering into an Administrative Order on Consent (AOC) with Talen Montana to address groundwater contamination from the Colstrip Steam Station's coal ash disposal ponds. Talen is working on pond and well upgrades that pertain to both the AOC and the Cleanup Criteria and Risk Assessment Rule. Touch on the Left-Hand Navigation for Documents for the latest details on the AOC and CCRA as well as the Facility Closure Plans.

DEQ’s issuance of the AOC was the subject of a challenge in state district court. Plaintiffs in that lawsuit and Talen have reached a settlement agreement that requires Talen to convert to the dry disposal of coal ash from Units 3 and 4 by July of 2022. Dry Disposal Plan by Talen Energy Dry Disposal Certificate Amendment Notice Final - 20 May 2016.

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Colstrip Steam Electric Station Coal Ash Ponds

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Dry Disposal Plan
By Talen Energy

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Solid and Hazardous Waste

Licensed the by Rosebud County Solid Waste District in August, 1994, the Rosebud County Class II Landfill serves Rosebud and Treasure Counties. The landfill is located approximately five miles north of Colstrip on Highway 39.

The facility is located on a 160 acre site with 22.3 acres developed for the disposal of municipal solid wastes. The facility accepts 10,000 tons of waste annually and has a design life of 46 years. The landfill features include a composite liner and leachate collection and removal systems. The facility also conducts semi-annual ground water monitoring and random waste load screening.

The Rosebud County Motor Vehicle Recycling Program collection site is also located at the landfill. There are no licensed private Motor Vehicle Wrecking Facilities in the Colstrip area. Also, see DEQ’s Landfill Locations & Materials Accepted Excel file.

Clean Air Act

Federal Mercury and Air Toxic Standards (MATS) rules

Title V Operating Permit


A Montana Pollution Discharge Elimination System (MPDES) permit is pending for the Rosebud Mine (MT0023965), which entails discharges into numerous receiving waters, including Armells, Cow, Stocker, Pony, and Spring Creeks.

The City of Colstrip community water system serves 2,300 people and the source is the Yellowstone River via Castle Rock Lake. Western Energy has a community water system serving 200 people and the source is groundwater.

(The City of Colstrip Water Treatment Plant) withdraws water from Castle Rock Lake, which is charged by water pumped thirty miles from the Yellowstone River. The city is authorized by DEQ to discharge filter backwash water to Castle Rock Lake. A pesticide general permit is also issued by DEQ for application to Castle Rock Lake to control algae growth.

The City of Colstrip has a (Waste Water Treatment Plant) with holding ponds, an oxidation ditch, and a sludge containment area. Reclaimed water is used on the Pine Butte Golf Course. A Phase One application is before DEQ for improvements on the system.

Talen Montana and DEQ have an Administrative Order of Consent (AOC) that requires an assessment of groundwater contamination stemming from leaking coal ash ponds. See the Colstrip Steam Electric Station Coal Ash Ponds for more information, or click on the Coal Ash tab.

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MPDES Permit
Montana Pollution Discharge Elimination System, Rosebud Mine MT 0023965

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Drinking Water Consumer Confidence Report Most recent report of Colstrip's drinking water.

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Categorical Exclusion for Proposed Wastewater Improvements

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