Gold King Mine

DEQ Water and Sediment Sampling Sites on the San Juan River

Spring 2019 Untreated Water Release

Extreme weather conditions and heavy snow knocked out power to the Gladstone Interim Water Treatment Plant (IWTP) at the Gold King Mine on March 13, 2019. Several avalanches along the road leading to the treatment plant prevented the operator from accessing the plant for several days. Snowpack in the San Juan Mountains near Silverton is 150 percent of normal, and avalanches have been common in recent weeks.

The IWTP plant operator monitored and ran the plant remotely on an emergency backup generator and intermittent line power following the storm. The pumps were able to run for roughly 20 hours before running out of fuel on the evening of March 14, 2019. The plant shut down, and untreated mine water began to flow at a rate of approximately 264 gallons per minute (gpm) into Cement Creek, then to the Animas River and on to the San Juan River.

Upon receiving the news of the plant shutdown, employees from the Utah Department of Environmental Quality (DEQ) along with teams from the U.S. Geological Survey (USGS) field offices in New Mexico and Moab headed to the Four Corners region to collect water samples.

Approximately 800,000 gallons of untreated mine water was released from the Gold King Mine between the evening of March 14, 2019, and the afternoon of March 16, 2019, when the plant went back online. The release was smaller than the 2015 release that deposited 3 million gallons of metal-laden mine water into the San Juan watershed over a shorter period of time.

The Environmental Protection Agency (EPA) has collected and treated discharge from the Gold King Mine at the water treatment plant since October 2015. The IWTP is located in the Cement Creek drainage basin and removes metals in the mine-impacted water through lime neutralization, precipitation, and flocculation.

A series of monitoring gages were installed along the Animas and San Juan Rivers following the 2015 mine release. Since 2015, Utah DEQ and its partner agencies have collected sediment and water samples in the San Juan River watershed on a regular basis to monitor water quality and assess impacts to the watershed.

Update March 29, 2019

DEQ collected water and sediment samples at four different locations on the San Juan River in March 2019. Water samples were screened against recreational, drinking water, agricultural, and aquatic-life criteria. Sediment samples were screened against recreational and aquatic-life screening values.

The tables below summarize the sampling effort and the exceedances that occurred. In the tables, blue cells indicate samples that were collected before the estimated arrival of the plume, and the orange cells indicate an exceedance of a water quality criterion or a screening value.

It should be noted that dissolved metal samples that were taken on March 16, 2019 – before the estimated arrival of the plume – may have been contaminated with particulate matter due to the difficulty of filtering samples with such a high content of sediment. The additional sediment in the samples may have resulted in the water-quality exceedances observed for lead, aluminum, copper, iron, and selenium in these pre-plume samples. The only sample to exceed water-quality criteria after the plume arrived was the aquatic-life use selenium value.

There were no recreational screening value water-quality exceedances for total metals or sediment screening value exceedances for recreation and aquatic life.


Update March 27, 2019

DEQ reviewed water-quality data collected by the Environmental Protection Agency (EPA) in response to the Gladstone Interim Treatment Plant discharge to determine the impact to downstream water quality in the San Juan River, Utah. DEQ confirmed EPA’s finding of elevated metal concentrations at the Cement Creek sampling location (4 MB) in Colorado, with concentrations steadily decreasing from upstream to downstream.

The most downstream site (Animas River at Rotary Park in Durango, Colorado [4 MB]) showed little change in metals concentration (4 MB) over the sampling period. Total metals load discharged by the release was not calculated due to the absence of flow and concentration data from the discharge effluent. An approximate calculation of dilution occurring between Cement Creek and the USGS Four Corners gage located just before the San Juan River enters Utah indicates that metals concentrations decreased significantly en route to Utah and likely did not exceed Utah’s water-quality criteria.

DEQ will review the water-quality and sediment data collected in the San Juan River from March 18 to March 20, 2019, when available, to confirm this finding. Based on the size and duration of the release and the concentrations observed at the most downstream sampling location in Durango, DEQ does not expect that additional precautions for using the water in Utah are warranted.”

Update March 25, 2019

On Friday, March 22, 2019, EPA released water-quality data (4 MB) from five sampling locations (4 MB) on Cement Creek and the Animas River in Colorado. These data are available at the Gladstone Interim Treatment Plant site profile. DEQ plans to analyze these data to determine the potential for impacts to water quality downstream on the San Juan River and will update the webpage with findings later this week.

  • See EPA Press Release on Sampling Data

Update March 18, 2019

On the evening of March 15, 2019, San Juan County cleared one lane of the county road leading to the IWTP. On the morning of March 16, 2019, the operator was granted permission to drive up to the plant. The operator was able to get the treatment plant successfully operating by early afternoon on March 16, 2019. The EPA Region 8 Bonita Peak Mining District team continues to coordinate with the plant operator to ensure the continued operation of the treatment plant.

At this time, the EPA anticipates that there will be no impacts to downstream drinking water or agricultural users from the short-term shutdown. Any impacts are expected to be localized and largely limited to aquatic life in the Animas River Canyon south of Silverton, Colorado.


Teams from DEQ, the U.S. Geological Survey (USGS), and New Mexico were dispatched immediately after receiving the news of the release and have been on site since March 16, 2019, to monitor the release and gather water and sediment samples. DEQ and USGS scientists collected samples on March 16, 2019, before the release reached the San Juan River. Results from these samples are expected by March 20, 2019.

Teams remain on site to sample and monitor the release, which is anticipated to reach the San Juan River between Sunday afternoon (March 17, 2019) and Tuesday morning (March 19, 2019). A DEQ team began additional sampling on the afternoon of March 18, 2019.

DEQ plans to visit four sites twice daily on March 19 and 20, 2019, to collect grab samples and sediment samples. DEQ is coordinating this sampling effort with USGS scientists who will collect depth-integrated samples at the same sites at the same time. The use of different sampling methods at the same sites is anticipated to produce a richer dataset.

Sample sites on the San Juan River match the 2015 sample locations, with the addition of a replicate sample for quality-control purposes:

  1. Four Corners (state line)
  2. Montezuma Creek
  3. Sand Island
  4. Sand Island (replicate for quality control)
  5. Mexican Hat

EPA collected weather-limited water samples at the bridge on Cement Creek below the water treatment plant and along the Animas River below Silverton and in Durango on March 15, 2019. These sample results are expected to be available on March 21, 2019.

Recreational Users:

The BLM has been in contact with the San Juan County Health Department, who is working with the Utah Division of Water Quality to monitor the San Juan River. The diluted wastewater is expected to reach the Utah border on Tuesday, March 19 and flow through the Bureau of Land Management (BLM)-managed recreational boating segment of the San Juan River between Montezuma Creek and Clay Hills over the following several days. Based on available information, the river segment remains open to boaters and no BLM recreation closures are currently in effect. The BLM always recommends that recreational users bring all of their drinking water while visiting the river and not rely on personal devices for filtration/purification of river water.

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