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On August 5, while investigating the Gold King Mine in southwestern Colorado, the U.S Environmental Protection Agency accidentally triggered the release of approximately three million gallons of acidic, metal-rich mine wastewater from the Gold King Mine into Cement Creek, a tributary of the Animas River. The Animas River flows south into the San Juan River, which is a tributary to the Colorado River. (Source: EPA)

Sample Collection in Multiple States
USGS scientists from several offices are providing scientific input following the release. For example, a USGS analysis of streamflow data from USGS streamgages along Cement Creek and the Animas River near Silverton, Colorado, showed that the release was approximately three million gallons, and these results were provided to EPA. Additionally, USGS scientists are studying various environmental effects of the release. Water and sediment samples are being collected along Cement Creek upstream from Silverton, downstream along the Animas River from Silverton to the confluence with the San Juan River, and downstream along the San Juan River in neighboring New Mexico and Utah.

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Researching Effects of Abandoned Mine Lands in the Animas River Watershed
The upper Animas River watershed near Silverton, Colorado, has been an area of extensive interdisciplinary USGS research on abandoned mine lands. Prior to mining in this area, the mineralized rocks were natural sources of metals and acidity to streams. Ancient, naturally-occurring ferricretes are surficial deposits cemented with iron-rich minerals that indicate acidic water has long existed near Silverton, Colorado.

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Historical mining contributed to the metals and acidity of streams in this area. Mining activities, including shafts, tunnels, and mine waste piles, exposed rocks and minerals to air and water, increasing release of metals and acid to groundwater and adjacent streams. The metals and acid in streams of the upper Animas River watershed today are derived from a combination of naturally mineralized and mining-related sources. For example, USGS investigations in the 1990s and 2000s indicated acidic water and elevated metal concentrations caused toxicity to trout for most of the length of the Cement Creek. USGS research detailed how the acidic metal-rich water in Cement Creek is strongly influenced by the geologic characteristics of the individual mines and naturally mineralized, unmined areas that drain into the creek.

Multiple USGS papers have been published about the environmental effects of unmined, mineralized areas and historical mine sites within the Animas River watershed. These reports collectively provide a critical environmental baseline against which the effects of the release can be assessed. The reports also provide crucial geological, geochemical, hydrological, remote sensing, ecological, and aquatic toxicological information that helps inform abandoned mine cleanup decisions within the Animas watershed.

For more than 20 years, scientists with the USGS have been studying the environmental effects of some of the estimated 200,000 to more than 500,000 abandoned mine sites throughout the country, including the Boulder River in Montana and the upper Arkansas River near Leadville, Colorado.

Next Steps: Start With Science
As the visible evidence fades from the August 5 Gold King Mine release, the USGS will continue working with partners to fully understand the immediate and lasting effects across the Animas River watershed and downstream waters. On August 18, the EPA announced that the U.S. Department of the Interior will lead an independent assessment of the factors that led to the Gold King Mine incident. It is anticipated that DOI will provide the assessment report to EPA and the public within 60 days.

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Ross Basin, Upper Cement Creek in Watershed Above North Fork Cement Creek