DEQ Press Releases

Harbage, Rebecca

DEQ Issues Approval of Remaining Report Concerning the Cleanup of Coal Ash Ponds at Colstrip Steam Electric Station

Approval Includes Selection of Remedy for Units 1&2 Stage I and II Evaporation Ponds and Response to Public Comments

HELENA—The Montana Department of Environmental Quality has  approved the Integrated Remedy Evaluation Report, Units 1&2 Stage I and II Evaporation Ponds, submitted by Talen Montana, LLC, and selected a remedy to address contamination at the Units 1&2 Stage I and II Pond area. 


“Today’s action is a careful decision based on our thorough analysis of the alternatives,” said DEQ Director Shaun McGrath.  


Talen, the operator of the Colstrip power plant, submitted the report in accordance with the 2012 Administrative Order on Consent (AOC) between DEQ and Talen. The AOC requires an investigation and remediation plan for groundwater contamination caused by leaking ash ponds.   


The Colstrip site is a complex contamination site that requires thorough hydrogeological analysis. For purposes of the AOC process, the site was divided into three areas: the Plant Site complex, the coal ash disposal ponds for Units 1&2, and the coal ash disposal ponds for Units 3&4. DEQ previously approved remedies for the Plant Site and the Units 3&4 ponds. 


The Remedy Evaluation Report for the Units 1&2 Area was split into two parts: the first part (Part One) addressed the existing groundwater contamination from historical pond seepage and was conditionally approved by DEQ in June 2020. The second part (Integrated Report) was submitted to DEQ by Talen in September 2020 and provided options for addressing the source of the contamination (the ponds).  


DEQ has reviewed Talen’s proposed alternatives for addressing the source of contamination and has selected Alternative 10 based on information provided in the Integrated Report. Alternative 10 consists of fully excavating the Stage I and Stage II Ponds in the Units 1&2 Area and relocating the ash to a new, lined impoundment above the water table on Talen property. This alternative also includes the components from the Part One Report that were previously conditionally approved by DEQ.  


Financial assurance from Talen is required under the AOC to cover the costs of the remedy; DEQ is requiring $285,438,000 million for Alternative 10. This brings the total site-wide financial assurance for remediation of the Colstrip ash ponds under the AOC to $485 million. 


Prior to selecting a remedial alternative, DEQ solicited public comments on the report from Sept. 21 to Oct. 26, 2020. A Responsiveness Summary that provides responses to the comments received is available on DEQ’s Colstrip website at:  


Copies of the reports are available at DEQ’s office at 1225 Cedar St., Helena; Talen Montana’s office at 303 N. Broadway, Suite 400, Billings; and the Bicentennial Library at 419 Willow Ave., Colstrip. The reports and DEQ’s approval letter are also available electronically by accessing the “documents” tab on DEQ’s Colstrip website. 

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