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Colstrip Steam Electric Station Coal Ash Ponds

DEQ is engaged in an enforcement action against PPL over groundwater contamination caused by leaking ash ponds at their Colstrip Steam Electric Station.  The steps both DEQ and PPL must take to address these problems are outlined in the Administrative Order on Consent, which both parties agreed to in 2012.  

This webpage includes the documents, maps, and other analyses of the Colstrip site related to the AOC.  Because this enforcement action involves complicated legal and environmental factors, DEQ has prepared a set of frequently asked questions about the Colstrip facility.  We recommend that anyone interested in DEQ's work at the Colstrip facility refer first to that brief introduction.    

To stay up to date with DEQ's work at the PPL Colstrip facility, or with other questions, email  We will add you to an email list which receives updates on public notices and other major announcements about this project.   

Administrative Order on Consent

The Administrative Order on Consent sets forth the process DEQ and PPL must follow to address groundwater contamination at the Colstrip site.  

You can download the entire AOC at this link, and view related documents below: 

Site Reports:

As a part of the AOC, PPL is required to submit analyses of the groundwater contamination at the Colstrip site.  These reports contain the results of groundwater testing performed by PPL in each of the three areas defined in the AOC: at the plant site itself, in addition to the two major pond complexes.  

Plant Site Reports and Related Documents:

Units 1 and 2/Stage I and II Evaporation Pond Site Report and Related Documents:

Units 3 and 4 Effluent Holding Pond Report and Related Documents:

In addition to the steps created by the AOC, DEQ has periodically worked with PPL to create plans to address issues as they arise.  You can view those plans at this link.  

Background Material:

Below are many of the agreements and decisions that precede the 2012 AOC agreed to by DEQ and PPL: 

 2014 Dam Inspection Reports:

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