Narrative
The Birchville Hydraulic Mine is located on unpatented BLM administered land but adjoins other large patented hydraulic and drift placer gold mines in the Birchville Mining District. The +33 acre mine site contains a 700+ foot long sluice box tunnel. The tunnel outlet has been blocked by a concrete bulkhead, forming a pit lake roughly 10 acres in size on BLM land. A large perennial pond- wetland area encompasses the margins of the pit lake. Initial water, sediment and biota samples have been collected to assess total and methyl mercury contamination values during FY02. It is likely that significantly levels of methyl mercury will occur in invertebrate, frog, and fish tissue samples, as occurs elsewhere in the Bear-Yuba watershed where hydraulic mine sediments are in contact with water bodies (See OEHA fish mercury contamination advisories for reservoirs in the Bear-Yuba watershed.). Consumption of mercury contaminated fish could pose a potential human health risk for the general public,.
Reclamation/Recommendations
1. Pit Pond - Mercury Contamination: Characterization:Characterization of mercury contamination levels in the hydraulic pit pond and associated wetland areas was initiated during FY2002 and includes initial sampling of water sediment, and biota to determine what levels of mercury concentration exist. Seasonal wetland areas in similar hydraulic pit settings elsewhere represent key sites for mercury methylization. Estimated cost $20,000
2. Public Access and Use:
Access to the site is currently restricted, due to private property easement restricting public access. The site is primarily accessed used by mining claimants.
4. Land Status and PRP search :
A potential responsible party (PRP) search will be initiated in FY 2002. The potential exists for a cooperative AML partnership between BLM staff and the mining claimant.
5. Restoration Methods Being Considered:
a. Tunnel/Pond Sediment Removal
If the pit lake contains significant levels of mercury in the sediments, water, and biota, the feasibility of draining the pit lake and removing sediments from the pit lake may be considered. Estimated cost $200,000.
Removal of sediment located on the tunnel floor and sidewalls and in the seasonal pond area would be accomplished using a high-pressure water system beginning in the farthest upstream areas. The mercury contaminated sediment would be collected in a sump and transferred into storage tanks for additional treatment. Any surface flows normally flowing through the tunnel would be diverted. After all the sediment is removed, an impervious cap would be applied to prevent further deposition of mercury into the tunnel floor fractures/crevasses. Water flow through the tunnel would be restored. Post-monitoring water sampling would be performed to verify that the tunnel outflow was still not contaminated. This sediment removal process was recently applied at another sluice tunnel site and proved effective Estimated cost $200,000.
b. Pond and Tunnel Bioremediation Method
Specific chemical or bacterial remediation processes may be applied to either remove methyl mercury or stop the mercury methylization process. Additional studies will be required to support pilot project applications. Estimated cost unknown.
Risks: Hg Contamination
AMLIS #: CA021800048
Location: N39 19 34, W121 09 2
Field Office: Folsom
Congressional District: 02
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