Gold King Mine Spill: Update on Animas River Health

Water Quality Program Staff display instrument that collects data every 30 minutes in the River.
pH summary data show the plume arriving at the Northern border of the Southern Ute Indian Reservation at 6 a.m. on August 7, yet pH values do not drop below 7.4
pH tolerance values of Animas River trout and other aquatic life are in between 6-9
Courtesy SU Environmental Programs Division
Courtesy SU Environmental Programs Division
Courtesy SU Environmental Programs Division
Courtesy SU Environmental Programs Division


On Aug. 7, 2015, EPA contractors working on the Gold King Mine accidentally triggered a release of approximately 3-million gallons of mine wastewater. The contractors were not prepared to control the release. The discharge, rich in toxic heavy metals and low pH, flowed into Cement Creek. Cement Creek joins the Animas River at Silverton and showed low pH and high metals content as a result of the spill.

The Southern Ute Indian Tribe was notified of the spill by the State of Colorado on August 3 and immediately enacted its emergency response team and alerted the State of New Mexico. The waste took approximately 3 days to reach the northern border of the Southern Ute Indian Reservation in the early morning hours of August 7.

The concern to aquatic life, human health, agriculture and recreation from the spill surrounds low pH values that can kill crops and aquatic life on contact, and high heavy metal concentrations, which when ingested, can cause adverse effects to humans and livestock. Metals pollution from mines comes in two forms, total and dissolved. Total metals are large molecules, often bound to sediment; this is the visible portion of the pollution that turned the Animas a shocking orange yellow. Dissolved metals are smaller, not visible and readily available for uptake by animals and plants and toxic at elevated concentrations.

The Silverton area has been releasing low pH and high metals water into the Animas for hundreds of years from natural process and by mining. Metals pollution had not reached the reservation because of dilution from tributary streams and because of buffering impacts of limestone outcrops in the northern Animas valley. Limestone increases pH and makes heavy metals less toxic to aquatic life.

To assess the impacts of the spill, the Southern Ute Indian Tribe’s Environmental Programs Water Quality Program (WQP) Staff began to collect pre-spill water quality and macroinvertebrate samples before the spill hit the reservation. In addition, WQP deployed instruments in the river that track pH, dissolved oxygen, temperature and conductivity at 30-minute increments. The WQP began coordination with EPA, Colorado, La Plata County and many other local entities to coordinate monitoring locations, analytes and other response. The WQP collected daily water samples from the river for two weeks following the spill, collected drinking well samples, continued monitoring of the continuous reading instruments, collecting post spill macroinvertebrate data.

To assess whether the Animas River has returned to normal levels, the WQP compiled historical data on the Animas for comparison and also looked at Colorado Water Quality Standards set to protect human health and the environment. The WQP has been collecting water quality data on the reservation since 1992 and is in the process of creating Tribal Water Quality Standards.

The WQP noted increased metals concentration in the Animas on the day of the spill that quickly rebounded to pre-spill concentrations: pH dropped on the reservation only slightly, and never went below pH 7.4.

Trout, for example, prefer pH in the range of 6-9. Water quality data from the spill showed elevated levels of total metals and little increase to dissolved metals. Standards set by Colorado and the EPA that protect human and animal health from immediate danger were exceeded for arsenic, lead and aluminum on August 7 only, then quickly rebounded to pre-spill levels.

Macroinvertebrate samples collected one day before the spill were compared to macroinvertebrates collected four days after spill shows no change in those populations.

While the data show little noticeable immediate impact to the Animas River, the WQP will be monitoring for many years to come to determine any long-term impacts. The WQP will be evaluating water chemistry, macroinvertebrates, river sediment, and fish tissue to understand any long-term impacts. The evaluation will last several years for specific impacts from the spill and will be ongoing for many years beyond that for normal monitoring activities.

Please contact the Water Quality Program with any questions about the spill, or with any other water quality concern you may have, 970-563-0135 .

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