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. The Conjecture Mine is one of five mine sites located in the Gold Creek drainage, Lakeview Mining District, Idaho Panhandle National Forests, US Forest Service (USFS). 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/USFS approach to address mine waste contamination found in the Gold Creek watershed.
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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, will enter 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.
Response activities, which are expected to require four months to complete, consist of the excavation of mine waste contaminated soil and sediment and consolidation beneath a soil cover at a nearby USFS repository; reconstruction of the Gold Creek channel; and grading, revegetation, and erosion protection of disturbed areas.