Cleaning up Contamination in Hard Rock Mine Lands
The abandoned Silver Ledge mine in the Upper Animas River watershed, Colorado. The Animas River watershed was one of two pilot watersheds studied as part of the USGS
Abandoned Mine Lands Initiative.
The U.S. Geological Survey (USGS) Abandoned Mine Lands Initiative is developing and demonstrating scientific knowledge and technologies that will assist Federal land management agencies to clean up contamination in areas near abandoned hardrock mines across the Nation. The Initiative is being conducted in two pilot watersheds, the Upper Animas River watershed in Colorado and the Boulder River watershed in Montana, where the USGS is partnering with the U.S. Forest Service, Bureau of Land Management, U.S. Environmental Protection Agency, and State agencies in Colorado and Montana. These agencies are using USGS scientific information to prioritize and design cleanup activities in the watersheds.
The Initiative's contributions to the abandoned mine land problem include:
- Tracer tests, in which a tracer such as a salt is put into a stream and its downstream movement is measured. Tracking how the salt is diluted in the stream gives information on how much water is being added to the stream. These tests are successfully identifying the largest sources of contamination from abandoned mine lands, and are enabling efficient targeting of cleanup activities.
- Water quality and flow measurements that define seasonal and other temporal variations in contaminant movement. Such studies show that zinc levels in the upper Animas River exceeded, on approximately 354 days a year, the standards proposed by the Colorado Water Quality Control Division.
- Methods to determine the environmental conditions that existed before mining began in order to establish realistic cleanup goals. In some mined areas, water quality was affected by the natural weathering of mineral deposits before mining occurred.
- Documentation of the downstream movement of metal contamination associated with ultra-fine particles that accumulate in the bottom sediment of rivers and streams. This method of contaminant migration was found to be a significant source of exposure of toxic metals to aquatic organisms.
- Findings that metal concentrations in fish and aquatic insects were higher than in the surrounding water and bottom sediments, indicating that metals (some of which are toxic) are accumulating in the local food chain.
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