Project Description:
A complex system of surface sluice cuts with an interconnecting sluice and drift tunnela exist at the Poore Mine. The Poore Mine represents was a moderate sized, historic hydraulic and drift placer gold mine operation dating from the 1870's. The principal sluice tunnel passively collects water and sediment from the adjacent hydraulic pit and underground drift working areas and discharges the mining waste material and mine water into Greenhorn Creek, Water and sediment samples taken from the surface and underground sluice sites indicate elevated levels of mercury contamination.
Previous/Existing Assessments:
The Poore Hydraulic Mine is located on unpatented BLM administered land but adjoins other large patented hydraulic and drift placer gold mines. (E.g. Jenny Lind, Gouge Eye Mines) The 70+ acre mine site contains a 800+ foot long sluice box tunnel containing high concentrations of elemental and methyl mercury in the tunnel sediments. The blocked inlet of the sluice tunnel has created several small seasonal and perennial ponds and wetland areas, which contain high levels of methyl mercury in the water and biota. The sluice tunnel and several inclined vertical shafts represent physical safety concerns to the public. Skin contact with the mine water discharge could pose a human health concern for recreational miners.
Reclamation/Recommendations:
1. Sluice Tunnel Characterization:
Collection of water and biota samples inside the sluice tunnel and seasonal pond was initiated in FY2000. the hydrological and geochemical data will be used in determining the best and most cost efficient method for controlling or eliminating elemental and methyl mercury. GPS equipment has provided better locational resolution of sluice tunnels and sluice cut locations with respect to published topgraphic maps. Bat surveys were also conducted, as well as assessment of the tunnel for potential bat habitat.
2. Pit Pond Characterization:
Characterization of the hydraulic pit ponds has included seasonal collection of biota and analysis to determine what levels of mercury concentration exist in tissue samples. Assessment of reopening the tunnel inlet portal will be undertaken, effectively eliminating the lowest elevation seasonal pond area within the hydraulic pit and one of the key mercury methylization sites. Removal of the pond may require compliance with Non-BLM government agency mitigation requirements.
3. Public Access and Use: Access to the site is currently restricted by installation of a gate. The site was previously used by recreational gold miners, marksman, and the general public. The risk for recreationists to be subjected to dermal contact with elemental mercury is high. Hydraulic mine sluice tunnel sites also pose physical hazard and chemical exposure risks to the general public. A mine gate, using bat friendly gate designs, has been erected at this site to deter public access into the sluice tunnel areas.
4. Proposed CERCLA cleanup actions:
Phase I CERCLA actions consisted of compilation of a Potentially Responsible Party (PRP) investigation, RSI (Removal Site Investigation) reports. A draft EE/CA (Engineering Evaluation/Cost Analysis) has been compiled and prooses a series of remedial options. A USGS technical team will continue monitoring the site.
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