Upper Blackfoot Mining Complex Cercla/Mike Horse Site

Regional Forester Tom Tidwell has issued the Action Memorandum and Final Engineering Evaluation/Cost Analysis (EE/CA) for the Mike Horse Dam and Impounded Tailings, Lower Mike Horse Creek, Beartrap Creek and Upper Blackfoot River Removal areas at the Upper Blackfoot Mining Complex site near Lincoln, Montana. The Action Memorandum identifies Site Wide Alternative 4 as the selected removal action. In general, Site Wide Alternative 4 includes removal actions at four subareas within the site, including:

  1. Mike Horse Dam and Impounded Tailings – Option 4
    The Mike Horse dam and impounded tailings would be removed from the Beartrap Creek valley bottom and placed in the Paymaster repository.
  2. Lower Mike Horse Creek – Option 3
    This option includes removal of all wastes from lower Mike Horse Creek and placement in the Paymaster repository.
  3. Beartrap Creek – Option 4
    This option includes removal of all concentrated tailings and removal of intermixed tailings within the active stream migration corridor, and placement of the wastes into the Paymaster repository.
  4. Upper Blackfoot River – Option 4
    This option includes removal of all wastes from the Blackfoot River floodplain including concentrated and dispersed tailings, and placement of these wastes in the Paymaster repository.

A more complete description of Site Wide Alternative 4, the individual removal options, and the rationale for this decision is found in the Action Memorandum below. The complete Final EE/CA and Administrative Record File for the project can be viewed at the Helena Forest Supervisor’s Office or Lincoln Ranger District. Copies of the EE/CA will also be available at the Lewis and Clark County libraries in Helena and Lincoln and are available to be retrieved from this website

The decision was guided by the criteria within the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA). The primary goal of the removal action is protection of human health and the environment through minimization of direct contact with contaminants and minimization of migration and mobility of contaminants within the environment. Assessment criteria for the evaluation of options within the Final EE/CA include effectiveness, implementability, and cost.

Changes Between Draft and Final EE/CA

The Final EE/CA follows release of a Draft EE/CA in July, 2006. Numerous public, agency and company comments were received on the Draft EE/CA and many changes were made between the draft and final document as a result. Primary changes include the addition of groundwater well data for the west side of the Mike Horse impoundment and an evaluation of groundwater in the vicinity of the impoundment, inclusion of two out-of-drainage repository sites in the repository evaluation section, revisions to removal options 3 and 4 for the Mike Horse dam and impounded tailings subarea, modifications to the streamlined risk evaluation, and revisions to the removal design concepts for the Mike Horse dam and impounded tailings subarea based on a stability analysis. As a result, the drawings for the design concepts have been modified for the impoundment options as well as the costs for each of these options.

What is Next

The Forest Service is using its authority under CERCLA to initiate this removal and to pursue accountability for the performance of work and reimbursement of costs from potentially responsible parties. These actions are ongoing. The Forest Service is also initiating diversion and dewatering of Beartrap Creek in 2007 in order to reduce the threat of a failure of the Mike Horse Dam in the short term. This work will be initiated in the Fall of 2007.

If you have any questions regarding this project and the attached Action Memorandum, please contact Amber Kamps, District Ranger, or Beth Ihle, Forest Geologist and On-Scene Coordinator, at the Townsend Ranger District, (406) 266-3425.

Mike Horse documents

Executive Summary - October 2015

2015 Technical Memorandum

Implementation Plan in Support of Petition of Adoption of Temporary Water Quality Standards of the Upper Blackfoot Mining Complex (2000)

Additional Upper Blackfoot Mining Complex Documents 

2006 Draft Engineering Evaluation/Cost Analysis (EE/CA)

July 2007 FINAL Engineering Evaluation/Cost Analysis (EE/CA)

Evaluation of Mike Horse Dam, January 2005, USFS (Romero)

Repository Siting Study for the Upper Blackfoot Mining Complex

Decision and Amendment to the 2007 Action Memorandum

Mike Horse Study Comments - 2011