Understanding the proposed re-operation of Idaho-Maryland Mine

The Sierra Nevada foothills are geologically interesting and rich in minerals, including gold. Grass Valley is a historic hard rock gold mining town built on top of legacy, abandoned mines. Idaho-Maryland Mine was the second most productive hard rock gold mine in the Sierra Nevada. Between 1867 and 1957, the mine went through five periods of activity that extracted a total of 2.4 million ounces from the gold-bearing quartz veins located underneath Grass Valley.

In November 2019, Rise Grass Valley Inc. submitted an application to Nevada County for a permit to re-operate the Idaho-Maryland Mine. From experience, The Sierra Fund has learned that operating a new gold mine on top of and around an old gold mine is complex and complicated. As a result, The Sierra Fund will be asking the County to take extra care as the evaluation of this permit moves forward.

The proposed re-operation of a mine in our area poses three central questions for the residents of Grass Valley to consider. (1) How would it benefit the community? (2) What are the impacts to the area? (3) What existing conditions must be addressed in order to allow re-operation of a mine less than two miles from downtown Grass Valley?

Environmental Impacts of Idaho-Maryland Mine

Water. Many miles of tunnels were built during prior mining operations at the Idaho-Maryland Mine site. When the mine was abandoned these tunnels filled up with naturally occurring water. To re-operate the mine, the area would need to be dewatered. This process entails pumping water from the old mine, treating the water to remove any toxic materials, and then discharging it into Wolf Creek. Proposed discharge rates are about 2,500 gallons per minute, a flow roughly equivalent to flood stage for the creek, until the mine is drained. After the initial dewatering, ongoing dewatering would send about 850 gallons per minute into Wolf Creek to keep the mine from refilling with water. The geology of this region that holds and transports underground water can respond unpredictably to dewatering and mine operations, potentially affecting local water resources. Mobilizing legacy contaminants in tunnels and in waterways with increased discharge can cause water quality problems.

Earth. Extracting gold produces tailings and waste rock, the byproduct of mine works. The scale of production is immense because gold yield is typically grams for every ton of ore rock excavated from a mine. The permit application describes a drill and blast regime beneath and beyond the boundaries of the property on Brunswick Road that would remove 1,500 tons of rock per day, operating 24 hours a day, 7 days a week for the life of the project. The permit states that half of the mined rock would be deposited at two sites on and near the mine. Haul trucks would deposit 1.4 million cubic yards of mining tailings on 31 acres of the Brunswick property where the mine is located up to their boundary near Mink Court and Elk Lane. One million cubic yards of mining tailings would be deposited on the 44-acre Centennial Industrial Site bordered by Idaho Maryland Road, Centennial Drive, and the DeMartini RV site. The permit application does not indicate how many years the disposal sites can receive mine tailings and what happens with the debris once these fill sites are full. Rise Inc. plans to sell mine tailings as engineered fill, utilizing highways 20 and 49 to transport the rock to potential customers. Mine tailings can be elevated in lead, cadmium, chromium, arsenic and other metals, posing a potential exposure risk.

Energy. Mining is a resource-intensive industry that requires large inputs of power. The permit application estimates power needs of 10 megawatts to run the mine with additional diesel back-up power generation capacity of 6 megawatts. One megawatt of power supplies 650-1000 homes with electricity. The proposed mine operation would re-inject 500 tons of processed mine debris as paste backfill each day into the blasted sections of the mine works to stabilize it. The backfill paste will use approximately 25 tons of cement daily, adding another 3 megawatts of power used to make the cement [1][2]. Although this power wouldn’t come directly from the local power grid, cement production, a resource-intensive industry, is responsible for 5-7 % of carbon dioxide emissions worldwide. The mine would contribute about 25 metric tons of CO2 daily solely from the production of cement required to backfill the proposed mine [3].  Mine operations would use up to 12,000 gallons of fuel per day, releasing another 120 metric tons of CO2 into the earth’s atmosphere daily. Mining for gold uses large amounts of energy to excavate and process vast quantities of rock in order to extract small amounts of precious metal.

Community Impacts from Idaho-Maryland Mine

While mining can be lucrative for those who control the operations, the benefits to local communities are less clear. One of the issues with extractive industries is that they do not take into account the social costs of projects. Gold is extracted and “goes away” as profit while traffic, noise, environmental, and other quality-of-life impacts are left to the community to deal with.

The application to re-operate the Idaho-Maryland mine states that 312 jobs would be created by the mine operations. Of those jobs, 242 jobs are specialized technical positions likely to be filled by people recruited from outside the area. The remaining jobs, truck transport of mine debris and mineral processing, could provide 70 jobs for current local residents. There would be a positive economic boost from mine employees spending their money locally.

It’s uncertain what local public revenue would come to our municipality from mining beyond property taxes and any sales tax levied on purchases made by people employed by the mine. California imposes $5 per ounce of gold mined as an assessment fee, collected by the California Department of Conservation for remediation of legacy mines on public lands. At the current gold price of around $1500 per ounce, the Department of Conservation would receive $3,333 for each million dollars of gold extracted by Rise Inc. None of this fee would come to Nevada County to remediate the impacts of this proposed mine operation. Public benefit from hard rock mining is small while the public burden is significant and traditionally goes unaddressed.

What can you do?

Become and stay informed about the proposed mine re-operation. Many local residents and organizations are thinking about the consequences of the proposed mine. Community Environmental Advocates Foundation is sponsoring a community campaign website at www.MineWatchNC.org. Mine permit application documents can be found at the County website mynevadacounty.com/2882/. The Sierra Fund will be monitoring and posting information on its website as the permit process proceeds.


[1] M Sheshpari (2015), A review of underground mine backfilling methods with emphasis on cemented paste backfill, Electronic Journal of Geotechnical Engineering 20 (13), 5183-5208

[2] Ernst Worrell, University of Utrecht Katerina Kermeli, University of Utrecht Christina Galitsky, Lawrence Berkeley National Laboratory, (August 2013), Energy Efficiency Improvement and Cost Saving Opportunities for Cement Making, EPA, Document Number 430-R-13-009

[3] Alireza Mokhtar, Mohsen Nasooti, A decision support tool for cement industry to select energy efficiency measures, Energy Strategy Reviews, Volume 28, 2020, 100458