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NEVADA CITY, Calif. December 15, 2017 – The Tahoe National Forest is requesting public comment on the Engineering Evaluation and Cost Analysis (EE/CA) for a non-time-critical removal action at the Empire Mine Site (Site) located on the Yuba River Ranger District in Sierra County. All public comments are welcome and will be accepted until the close of business January 16, 2018. Following this 30-day public comment period, a final decision will be made by the Pacific Southwest Region’s Regional Forester and documented in a Removal Action Memorandum identifying the removal action decision.
The purpose of the EE/CA is to present a detailed analysis of cleanup/removal action alternatives that can be used for decision-making. The analysis presented in this document includes discussion of site background information, a summary of the site investigation, a preliminary risk screening, applicable or relevant and appropriate requirements (ARARs), removal action objectives and goals, and the analysis and comparison of removal action alternatives.
The Empire Mine site (no relation to Empire Mine State Park in Grass Valley, California) is the location of a historical gold mine, mill and associated tailings ponds in a remote area of Sierra County, approximately nine miles north/northeast of the town of Downieville on the Yuba River Ranger District of the Tahoe National Forest. The Empire Mine lies along the east side of Pauley Creek, which provides drinking water for the residents of Downieville. The U.S. Forest Service is the federal agency in charge of the Site.
Empire Mine is an underground gold mine first established in approximately 1852 that has been mined intermittently through current day and produced over $2 million in gold. In 1905, a 25-stamp mill, chlorination plant, and reverberatory furnace were located at the Site. The focus of the EE/CA are waste rock along the access road and the fine grained tailings on and downhill of the mill site. Waste rock containing elevated concentrations of arsenic and lead are stockpiled onsite adjacent to the access roads. A tailings pile dubbed the “Red Dirt Pile” contains concentrations of metals that include antimony, arsenic, cadmium, lead, mercury, nickel, selenium, and silver substantially above background levels. The Red Dirt Pile is believed to be a collapsed chlorination plant used to extract gold from the crushed sulfide-bearing ore that was processed through the stamp mill and reverberatory furnace.
The Empire Mine is located within “Gold Valley,” which is heavily used by forest visitors for recreational uses such as hiking, fishing, hunting, backpacking, mountain biking and off-highway vehicle use (including snowmobiles). The area contains several developed forest system trails popular with mountain bikers and off-road vehicles.
The presence of arsenic, cadmium, cobalt, lead, mercury, nickel and silver in waste rock and tailings pose potential risks to wildlife at the Empire Mine. Achieving the preliminary Removal Action Objectives (RAOs) will ensure humans and wildlife are protected from elevated metals concentrations in source materials (i.e., the Red Dirt Pile) at the Site.
Based on investigation findings and preliminary risk screening, the Forest Service is exercising its authority as lead agency under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) to undertake a non-time-critical removal action at Empire Mine that best meets the following RAOs:
- Reduce exposure of humans to: a) tailings in the Red Dirt Pile area; and b) waste rock that contains metals at concentrations exceeding human health screening criteria stockpiled on site beside the access roads
- Reduce the risk of erosion and/or reactive dissolution from: a) tailings in the Red Dirt Pile area; and b) waste rock stockpiled on site beside the access roads, which could get into surface waterways
These RAOs will be achieved through excluding or removing mine waste rock stockpiles and the Red Dirt Pile and stabilizing the remaining substrate to prevent erosion. Physically excluding or removing the source of contamination (i.e., the reverberatory furnace and wooden platform with chlorination tanks) will reduce the possibility for the source of contamination to spread to a wider area.
Based on available site information and data, three types of general response actions were considered for the Empire Mine:
- No Action
- Engineering Controls
- Offsite Disposal
The following removal action alternatives were identified for Empire Mine based on the general response actions and screening discussed in the EE/CA and are listed in order of feasibility:
- Alternative 1: No Action
- Alternative 2: Dispose of tailings and mine waste rock in a lined repository constructed onsite
- Alternative 3: Cover the tailings, reverberatory furnace, and mine waste rock in place
- Alternative 4: Remove tailings and mine waste rock for offsite disposal
The removal action alternative recommended in the EE/CA for the Empire Mine is Alternative 3. This alternative is considered the most cost effective remedy while meeting all of the RAOs. The final remedy will be selected by the Forest Service after the public comment period.
The purpose of the EE/CA is to present a detailed analysis of cleanup/removal action alternatives that can be used for decision-making. The EE/CA is available for review on-line at: http://bit.ly/2BnMu40. Comments can be sent to: Tahoe National Forest, Attn: Rick Weaver, 631 Coyote St., Nevada City, CA 95959.