Stimson-Bonner Mill PCB Site

April 2004 - Looking upstream on the Blackfoot River at the Bonner Mill, Bonner Dam, and Cooling Pond area. PCB originated from inside the old stud mill (yellow building).

March 2011 - Phase I construction, removal of the stud mill PCB source area and cooling pond area.

June 2014 - Reclaimed Blackfoot River and Bonner Mill area after the Bonner Dam removal and the Stimson Phase I, II, and III PCB removal actions were completed.

Please click on the tabs below for more information on the Stimson-Bonner Mill PCB Site.


The Bonner Mill Cooling Pond cleanup project is located in Bonner, Montana, along the Blackfoot River. In the early 1880s, the first logs were cut at the Bonner mill site and shipped to the mining operations in Butte. Over time, the Bonner mill site owners built and operated a “cooling pond,” which actually extended out into the Blackfoot River. In 2006, DEQ discovered contaminants (PCB) in the sediments of the cooling pond. The Department of Natural Resources & Conservation determined that because of the removal of the Bonner and Milltown dams immediately downstream from the cooling pond area, the berm of the cooling pond would fail during the next 100-year high flow flood, washing the PCBs downstream. Working with DEQ, Stimson Lumber entered into an Administrative Order of Consent in 2010 to remove the PCB contaminated areas threatening the Blackfoot River. Between September 2010 and April 2016, contaminated soils and debris was removed from the site and shipped to landills or an on-site repository; the river was restored and no longer does a threat from PCBs exist from areas it once did. This webpage provides links to public fact sheets and updates throughout the life of the project.




Current Activities

No public input received on a Draft Plan to Remove Wastes at the Bonner Mill Site Repository located in Missoula, MT


The Montana Department of Environmental Quality (DEQ) requested public input on a draft plan submitted by Bonner Property Development, the current landowner of the site, to remove waste at the Bonner Mill Site Repository and dispose of the waste at the Republic Landfill located in Missoula, MT.   Currently, the repository is performing as designed and remains protective of human health and the environment.  DEQ is not requiring any party to remove or alter the repository. DEQ has not approved any amendment or modification to the current restrictive covenants at the site. Public input was accepted until 5:00 p.m. on October 9, 2020. DEQ received no public input. 


With the close of a request for public input, DEQ is currently reviewing the plan. DEQ’s review of the submitted draft plan will ensure that the proposed work will not conflict with ongoing work at the facility and that the work conducted will not spread, worsen, or otherwise exacerbate the PCB contamination. DEQ will review the plan to guarantee that all other relevant factors are considered for protectiveness of human health and the environment and that wastes are disposed of in a permitted landfill. If appropriate after such on-going review, DEQ may require revisions and additional information or approve a detailed work plan outlining the proposed work.


The draft plan documents are part of the administrative record.  Site documents may be requested here:


Keith Large

Project Manager
P.O. Box 200901
Helena MT  59620-0901
(W) 406-444-6569 (C) 406-431-2253