Iron Mountain Mine Superfund Cleanup

Sacramento Valley Region

Iron Mountain Mine Superfund Cleanup

  • Location: Spring Creek, tributary to Sacramento River near Redding, Shasta County
  • Project Sponsor: EPA
  • Time Frame: 1983–2009
  • Cost: $300 million (to date)
  • Project Objective:
    • Remediate the discharge of acid mine drainage from IMM and the problems of heavy metal contamination in the Sacramento River
Putting the Iron Mountain Mine Problem in Perspective

The acid mine drainage from IMM is among the most acid- and metal-laden water anywhere on Earth. Prior to the cleanup, the heavily worked mines on Iron Mountain discharged, on average, 650 pounds of copper, 1,800 pounds of zinc, and 10,000 pounds of iron per day. For comparison, the IMM discharge was at least equal to all the combined industrial and municipal discharges to the San Francisco Bay and Delta Estuary System. The IMM discharge was more than twice the combined discharge from the 28 largest inactive mines in northern California. The IMM discharge was equal to about one fourth of the entire national discharge of copper and zinc to surface waters from industrial and municipal sources. The IMM discharge was the largest discharge to surface waters in the nation identified under the Clean Water Act §304(l) program for cleanup of impaired waters of the United States.

Early in its history, IMM was famous for being the most productive copper mine in California and one of the largest in the world. In recent years, the legacy of mining at IMM turned its fame to infamy, as the site became known as the largest source of surface water pollution in the U.S. and the source of the world’s most corrosive water.

IMM is located in Shasta County approximately 9 miles northwest of the city of Redding. The IMM Superfund site encompasses 4,400 acres and includes several individual underground mines, a former flotation mill, a mining ore railroad loading station, Spring Creek Reservoir, and the Spring Creek arm of Keswick Reservoir. While the Shasta County copper mining era peaked in the early 1900s, IMM continued operations until 1963. Nearly 100 years of mining left numerous waste rock and tailings piles and an extensive network of underground tunnels. The fractured bedrock above the underground workings provided an effective means for air and water to reach the enormous sulfide deposits in the mountain. Researchers call Iron Mountain a worst-case scenario with regard to formation of acid mine drainage. The acidic drainage from IMM flowed into adjacent streams and then into Keswick Reservoir, a run-of-river reservoir on the Sacramento River below Shasta Dam. As early as 1900, the California Fish Commission investigated fish kills in the Sacramento River attributed to pollution from IMM. State records document more than 20 fish-kill events in the river since 1963. Those harmed included all four runs of Chinook salmon, steelhead, and resident trout.

Remediation efforts began with the 1963 completion of Spring Creek Reservoir, intended to prevent mine sediment from entering Keswick Reservoir and to regulate the quantity of mine drainage entering the Sacramento River. This was only marginally effective, and periodic events of toxicity in the river continued. In 1975, the RWQCB initiated enforcement action against the current mine owners and in 1983, IMM became an EPA Superfund Site. Many years of site assessment, further litigation, and alternative project plans followed. In 1994, a lime neutralization treatment plant was constructed to collect and treat all drainage from the mine’s underground workings (Richmond and Lawson Tunnel portals), effectively eliminating the largest source of acid and metal discharge. Numerous other projects were completed, such as diverting clean water around the mine workings, sealing waste rock and tailings piles, and constructing a large reservoir on Slickrock Creek to collect diffuse mine seepage and deliver it to the treatment plant.

A final remediation component was completed in 2010 that involved dredging and removal of contaminated sediment that had accumulated over the years in the Spring Creek arm of Keswick Reservoir.

More than 20 years of work by EPA, other federal and state agencies, and responsible private parties— much of it underwritten by Superfund—is finally paying off in a big way. Remediation and pollution control activities now neutralize almost all the acid mine drainage and control 95% of the copper, zinc, and cadmium that used to flow out of Iron Mountain into nearly streams and then into the Sacramento River. EPA and the state secured funding from one of the site’s previous owners in one of the largest settlements with a single party in Superfund history. The settlement terms should enable continuous operation and maintenance of the treatment facilities for the foreseeable future.