Berkeley Pit & Flooded Mines

The main features of the Butte Mine Flooding Operable Unit and the Berkeley Pit. Map from the EPA Five Year Review Report for the site (2011).

The main features of the Butte Mine Flooding Operable Unit and the Berkeley Pit. Map from the EPA Five Year Review Report for the site (2011). Click on the map to view a larger version.

Together, the Berkeley Pit and the historic underground mines of Butte, which have been flooded since groundwater pumps were turned off by ARCO in 1982, form the Butte Mine Flooding Operable Unit (BMFOU). EPA and the state of Montana are concerned about rising levels of contaminated mine water in the abandoned Berkeley Pit and connected underground mine workings that could eventually migrate into the shallow aquifer under urban Butte and into Silver Bow Creek. Berkeley Pit water is acidic and contains high concentrations of heavy metals. As of 2009, the Pit contained over 40 billion gallons of contaminated water.

The Berkeley Pit and connected underground mines have been filling with toxic water since 1982.

The Berkeley Pit and connected underground mines have been filling with toxic water since 1982.

The investigation of the Berkeley Pit has been completed and the remedy calls for:

  • Permanent control of surface inflow into the Pit
  • Maintenance of the water level in the Berkeley Pit system via a pump-and-treat system
  • Continued control of the West Camp/Travona System, which is connected to an aquifer separate from the Berkeley Pit
  • Implementation of an extensive compliance monitoring program
  • Implementation of institutional controls to restrict access to contaminated bedrock aquifer waters, as well as increased public education efforts

The complete Record of Decision (ROD) for the site can be downloaded at the link below, or via the Superfund Library.

 Record of Decision for the Butte Mine Flooding Operable Unit (including the Berkeley Pit) (1994)
938.4 KiB
1179 Downloads
Details...

The Potentially Responsible Parties (PRPs) started inflow control (average 3.8 million gallons per day) in April 1996. Controlling inflow has cut the rise rate in the Berkeley Pit by 50 percent. This inflow is treated with lime and used as makeup water in the present mining operation.

A treatment plant, known as the Horseshoe Bend Water Treatment Plant, was constructed in 2003 near the Pit. Currently, it is used to capture and treat inflow, but does not treat groundwater or water present in the toxic Berkeley lake. Prior to the water reaching the critical level where it could spread, the plant will be expanded to handle additional capacity, and then used to maintain the water level below the critical point. Currently, it is projected that water levels will approach the critical point around 2022 or 2023.

Groundwater movement and features in the Butte Mine Flooding Operable Unit and under the Butte Priority Soils Operable Unit. Map from the EPA Record of Decision (ROD) for the site (2006).

Groundwater movement and features in the Butte Mine Flooding Operable Unit and under the Butte Priority Soils Operable Unit. Map from the EPA Record of Decision (ROD) for the site (2006).

 

Monitoring wells for the alluvial (shallow) aquifer in the Butte Mine Flooding Operable Unit and around the Berkeley Pit. Map from the EPA Five Year Review Report for the site (2011).

Monitoring wells for the alluvial (shallow) aquifer in the Butte Mine Flooding Operable Unit and around the Berkeley Pit. Map from the EPA Five Year Review Report for the site (2011).

 

Monitoring wells for the bedrock (deep) aquifer in the Butte Mine Flooding Operable Unit and around the Berkeley Pit. Map from the EPA Five Year Review Report for the site (2011).

Monitoring wells for the bedrock (deep) aquifer in the Butte Mine Flooding Operable Unit and around the Berkeley Pit. Map from the EPA Five Year Review Report for the site (2011).

Five Year Review (2010-2011)

The EPA Five Year Review Report for the site and associated appendices can be downloaded using the links below, or via the Superfund Library.

  5-Year Review Report for SBC/Butte Area Superfund Site - Volume 3: Butte Mine Flooding Operable Unit (June 2011)
644.3 KiB
732 Downloads
Details...
  5-Year Review Report for SBC/Butte Area Superfund Site - Volume 3, Appendix A: Site Inspection Photographs & Monitoring Well Inspections (June 2011)
1.5 MiB
691 Downloads
Details...
  5-Year Review Report for SBC/Butte Area Superfund Site - Volume 3, Appendix B: Responsiveness Summary (June 2011)
96.3 KiB
621 Downloads
Details...
  5-Year Review Report for SBC/Butte Area Superfund Site - Volume 3, Figures (June 2011)
2.1 MiB
720 Downloads
Details...

 

Further Exploration

 

Leave a Reply

Your email address will not be published. Required fields are marked *

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <strike> <strong>