DEQ Press Releases

Driscoll, Paul

DEQ Issues Responses to Public Comments and Conditional Approval for Colstrip

HELENA – The Montana Department of Environmental Quality has responded to public comments and issued a conditional approval for Colstrip’s Revised Remedy Evaluation Report, Units 3&4 Effluent Holding Pond (EHP).


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 order requires an investigation and remediation at the facilities related to groundwater contamination caused by leaking ash ponds. 


DEQ selected Talen’s proposed “Alternative 4” remedy, with some modifications required. For this reason, DEQ is providing conditional approval of the report. Talen must complete the contingencies requested by DEQ before the report will be granted final approval. Talen is still required to submit financial assurance in the amount of $107 million.


The selected remedy consists of installing additional capture wells and a series of paired clean water injection wells that help remove the less mobile contaminants currently stuck in the aquifer. Talen will also dewater the ponds and close the ponds with a geosynthetic cap —t hese measures will prevent future seepage from the ponds. The contingencies that Talen must complete include:


  • Conduct a pumping test on the underdrain to ensure it will completely dewater the ponds. If the underdrain will not be effective, additional methods will be required (ex: well points) to dewater the pond in a timely manner.
  • Provide additional information to DEQ about the water storage capacity at the 3&4 ponds to ensure the underdrain can be turned on as soon as possible. If there is not enough storage for the underdrain to be turned on by 2021, additional storage will need to be constructed.
  • Additional data needs to be collected to support the proposed predicted timeframe for Monitored Natural Attenuation, including geochemical data from pond leachate and aquifer solids beneath the ponds that may act as a secondary source of contaminants. This will help determine the timeframe and how long active remediation (injection and capture) needs to continue.
  • Provide more detail regarding the water table below the ponds during capture/injection system operation and after the system shuts down, to demonstrate that the ash will not act as a long-term source of contamination due to continued contact with groundwater.
  • Install additional capture and injection wells as appropriate. If data indicates the remedy would benefit from running the injection and/or capture wells for a longer duration, financial assurance will be requested to keep the system running.


DEQ solicited public comments on the report from Oct. 11-Nov. 22, 2019. A Responsiveness Summary that provides responses to the public comments is available on DEQ’s Colstrip website:


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 by accessing the “Documents” tab on DEQ’s Colstrip website.


For questions, please contact Sara Edinberg, DEQ Project Manager, at:

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