Spring Creek Debris Dam is an earthfill dam on Spring Creek, a tributary of the Sacramento River, in Shasta County in the U.S. state of California. Completed in 1963, the dam, maintained by the U.S. Bureau of Reclamation, serves primarily to collect severe acid mine drainage stemming from the Iron Mountain Mine. The dam forms the Spring Creek Reservoir, less than long. Spring Creek and South Fork Spring Creek flow into the reservoir from a watershed. The dam is directly upstream from the city of Keswick, California and the Keswick Reservoir. The operation is part of the Trinity River Division of the Central Valley Project.
The primary purpose of the Spring Creek Dam was to collect acid mine drainage from the old Iron Mountain Mine, which was heavily polluting Spring Creek and its tributaries. The dam was built in response to these pollutants that were contaminating the Sacramento River, the primary water supply for millions of Californians. Although the watershed is small in comparison to that of the Sacramento River, the stream is among the most polluted and acidic in the world.
The dam and reservoir, along with other treatment structures built at and below the mine, have successfully reduced the dry weather pollution of Spring Creek by up to ninety-five percent. Problems, though, still occur mainly in the form of large uncontrolled spills from the reservoir. Several concerns about the structural integrity and safety of the dam, both physically and biologically, arose in the 1990s. Emergency releases from Shasta Lake, often in the value of thousands of acre feet of water, have occurred from time to time to dilute massive acid spills from the Spring Creek drainage.
History
Mining
The Iron Mountain Mine, the most productive copper mine in California in at least one point along its history, operated along the banks of two Spring Creek tributaries, upstream from the current dam site, from 1879 to the 1960s. The mine extracted iron ore, silver, gold, copper sulfide ore, and pyrite from a rock formation dating to approximately 780,000 years ago. The potential of a mine at the site was discovered in 1860, when two men, surveyor William Magee and settler Charles Camden, discovered an extensive iron ore deposit along one of the tributaries of Spring Creek. In 1879, silver was also discovered at the site, and the mine was begun. The ownership was transferred to Mountain Mines Ltd., a London company, in 1894. At the very end of the 19th century, Iron Mountain Mine took blames for several fish kills in the Sacramento River. Nevertheless, mining activity continued, and by 1928, 600 tons of ore were being extracted from the site per day.
The still continuing problem of Iron Mountain Mine runoff has once been described as:
Events prompting construction
The construction of Shasta Dam and its afterbay (regulating downstream dam), Keswick Dam, in 1943 and 1950, respectively, severely impaired the capability of the Sacramento River to flush away pollutants from the mine. Acid mine drainage flowed, unfettered, down Spring Creek directly into the Keswick Reservoir, depositing contaminated sediment and turning a portion of the water a rusty red shade. Previously, the water would have continued down the creek into the river, and flushed to the Pacific Ocean. The pooling of the water, however, made it extremely difficult for the pollutants to be removed. From 1955 to 1962, open pit mining began on the site. At its peak, the mine discharged 5 tons of iron, of copper, and of zinc into the stream per day. By then, the water flowing down the drainage was so contaminated that it necessitated the construction of a holding dam, the Spring Creek Dam.
Spring Creek Dam was begun in 1961, when a company named Gibbons and Reed was awarded the contract. The clearing operations began in July of that same year, and the dam was officially dedicated by the Bureau of Reclamation on September 12, 1961. Construction of the dam began on October 20, 1961, with the placing of the dam embankment, which at least partially consists of acidic sediment dredged from Spring Creek. Riprap was laid on the upstream face of the dam beginning November 9 of that year. In 1962, a series of labor strikes impacted communities in the Central Valley, also affecting construction of the dam, which was temporarily halted on May 3 of that year. After work restarted on June 26, pervious core material for the dam was soon out of supply, so impervious material was used to complete the dam core.