DEQ Press Releases

Harbage, Rebecca

DEQ Issues Response to Public Comments and Conditional Approval for Colstrip Report

HELENA—The Montana Department of Environmental Quality has responded to public comments and issued a conditional approval for Colstrip’s Revised Remedy Evaluation Report – Part One, Units 1&2 Stage I and II Evaporation Ponds.


The report submitted by the operator at Colstrip, Talen Montana, LLC (formerly PPL Montana), is required under the 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 has been 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 has been split into two parts: the first part (part one) addresses the existing groundwater contamination from historical pond seepage, and the second part (part two) will address the source of the contamination (the ponds). This was done to ensure DEQ could collect financial assurance for the aspects of the remedy that were known to be necessary (remediation of existing groundwater contamination), while additional work continues to determine the most effective method of controlling the contamination source.


DEQ is providing conditional approval of the part one report, authorizing only those components that can be implemented regardless of the method(s) needed to control the source of contamination that will be selected in part two. Talen’s proposed alternative for part one included expansion of the existing groundwater capture system, implementing clean water flushing using injection wells, dewatering two of the ponds (A and E Cells) and capping and closing the Stage II Ponds.


DEQ is approving the installation of additional capture wells, new clean water injection wells and dewatering of the A and E Cells in the Stage II Pond. This conditional approval will require Talen to submit financial assurance in the amount of $16,231,270.


DEQ is requiring Talen to evaluate excavation of the Stage II Ponds, in addition to the Stage I Pond, in part two, so DEQ is not approving capping the Stage II Ponds as part of the remedy. Additionally, the horizontal capture well proposed to be installed across the Stage I dam will not be approved, as this dam may need to be removed if the Stage I Pond is excavated and relocated.


DEQ solicited public comments on the report from Nov. 14 to Dec. 16 last year. A Responsiveness Summary that provides responses to the public comments is available on DEQ’s Colstrip website at:


Copies of the reports are available at DEQ’s office at 1225 Cedar Street, 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 conditional approval letter are also available electronically by accessing the “documents” tab on DEQ’s Colstrip website.

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