United States Environmental Protection Agency
Region X
POLLUTION REPORT

Subject: 

The Conjecture Mine is a historic silver and lead mine located on Gold Creek, about 6 miles south of Lakeview, Bonner County, Idaho.  Gold Creek is a perennial stream that flows into Lake Pend Oreille.  Mining wastes at the Conjecture Mine site are located partially on private and partially on National Forest System (NFS) lands.  This action is a continuation of a comprehensive EPA/US Forest Service (USFS) approach to address mine waste contamination found in the Gold Creek watershed.  

Mine operations occurred sometime after 1894 and continued periodically until 1963.  Mining was conducted underground on a patented claim and adjacent NFS land, and mining wastes in the form of waste rock and mill tailings were disposed on both private and public lands.  Much of the mine waste found on private land was produced intermittently from 1894 through 1951.  The Conjecture Mine site is situated near the headwaters of Gold Creek and occupies more than one-third mile of Gold Creek.  The upper portion of the site contains four large waste rock dumps, scattered deposits of disturbed and eroded materials, and stream sediments.  

The site is mixed ownership.  USFS, exercising its CERCLA authority as to the public portion of the site, entered into an Interagency Agreement with EPA to authorize work and to reimburse EPA for costs associated with cleanup of mine waste contaminated materials found on public land.  EPA is addressing mine waste contaminants found on private property.  Potential human health and environmental impacts from historic mine wastes present at the Conjecture Mine site include public health and safety risks, increased metal concentrations in surface water, and increased sediment load to surface water.

All project activities were completed on 21 September 2007, including: excavation of mine waste contaminated materials with consolidation at the mine waste repository; installation of the repository protective barrier consisting of soil and an HDPE liner; stabilization of all disturbed areas, including seeding and placement of woody debris; and obliteration of temporary access roads.

Approximately 22,660 cubic yards of mine waste contaminated materials were removed from the private lands, and approximately 14,600 cubic yards of mine waste contaminated materials were removed from the public lands.

Approximately 8,360 cubic yards of borrow source materials, including crushed rock and topsoil, were placed on private lands, and 33,300 cubic yards were placed on public lands. In addition, approximately 15,080 cubic yards of topsoil were placed on the repository as part of the protectice barrier.

None - All project activities are complete.

None - All project activities are complete.

None.