The Walloupa East sluice tunnel is located on both unpatented BLM administered land and adjoining patented hydraulic placer gold mines. The sluice tunnel outlet is located on BLM administered land and the inlet is located on fee simple property. The mercury outlet site has been subjected to water, sediment, and biota sampling and is known to contain concentrations of elemental and methyl mercury. The sluice tunnel portal is ungated and represented a potential physical safety concern to the public. Skin contact with the mine water discharge or sediments could pose a human health concern for recreational miners.
Site Restoration Considerations
1. Sluice Tunnel Characterization:
Collect data on the geological, hydrological and biological resources inside the sluice tunnel. Sampling was initiated in FY 2000. The geological and hydrological information will be used in determining the best and most cost efficient method for controlling or eliminating the production of methyl mercury. Estimated costs $25,000.
2. Public Access and Use:
Access to the site is currently unrestricted. The site is primarily accessed used by recreational gold miners, rockhounds, and the curious. The risk for recreationists to be subjected to dermal contact with elemental mercury is high. Hydraulic mine sluice tunnel sites also pose a high risk to the general public. Mine gates, using bat friendly gate designs, would be erected at this site to deter public access into the tunnel areas. Estimated cost $15,000.
3. Land Status:
A potential responsible party (PRP) search will be initiated in FY 2002
to determine past and current owners. The opportunity to develop a cooperative mine restoration partnership between the fee simple owner and the county resource conservation district will be pursued.
4. Restoration Methods Being Considered:
a. Tunnel Sediment Removal
Removal of sediment located on the tunnel floor and sidewalls
would be accomplished using a combination of mechanized underground mine equipment (mucker) and 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 the tunnel floor 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 $100,000.
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 or generation process that occurs within the sediments on the tunnel floor. Additional studies will be required to support pilot project applications. Estimated cost unknown.
c. Bypass Tunnel Water Flow - Remediation Methods
In most hydraulic placer gold mine sluice tunnels, water discharge is derived either from seepage or from historically redirected surface-water courses or both. Recreational miners can cause a mercury release by disturbing mercury-rich sediments while mining in the tunnel environment. Stopping public access into the tunnels using well-constructed bat gates and redirecting tunnel discharge water away from the anaerobic tunnel environment could more effectively control downstream mercury transport. Estimated cost $10,000.
Risks: Water Quality, Physical Safety
AMLIS #: CA020180007
Location: N39 12 01, W120 52 10
Field Office: Folsom
Congressional District: 02
