DENVER - An independent study of water quality in the Animas River after the Gold King Mine spill shows major human health concerns were short-lived, though slight spikes in pollution might occur with runoff.
Mountain Studies Institute, a nonprofit scientific research organization with an office in Durango, found a spike in metals as the orange plume passed through Durango on Aug. 6. But that spike quickly returned to conditions similar to how the river looked before the incident, according to samples.
"We tried to digitalize the data so that people can ... come to their own conclusions about whether they're comfortable with those numbers or not," said Marcie Demmy Bidwell, executive director of the institute.
"There's currently a 'distrust' for government that exists in our community, no matter what," she continued. "I can't answer the question for people whether they should trust their government on that versus everything else."
The plume was caused from an error by an Environmental Protection Agency-contracted team on Aug. 5. During excavation work to begin restoration of Gold King, the team accidentally released about 3 million gallons of old mining sludge into the river.
Early tests released by federal, state and local government agencies found initial spikes in metals, including lead, arsenic, cadmium, aluminum and copper. But the river returned to either nondetectable or pre-plume levels within a week.
Tests released Saturday by Mountain Studies Institute reflect similar data distributed after government testing. The results represent sampling at Rotary Park from Aug. 6 through Aug. 11. The data results are from samples taken from the Animas before the arrival of the Gold King plume, during the event and several days after the plume passed.
MSI was the only group taking samples from Rotary Park. It has been contributing as part of a unified response effort along with government agencies.
"At these levels, you would need to drink 2 liters of Animas water four days a week, for 16 weeks, to possibly experience adverse, noncancerous effects of those metals over a long period of time, years later," MSI's report states.
A slight increase in metals from a sample taken at noon Aug. 9 was observed, though it did not exceed toxic water-quality levels. Researchers believe the increase was caused by more water flow after rain Aug. 7.
"This slight uptick speaks to the lingering concerns post-plume from the deposited sediments. We would expect to see slight increases in metal detections as we experience precipitation events this fall and with spring runoff next year," the report states.
The study focused only on risks to human health, not impacts to fish and other wildlife. Colorado wildlife officials on Wednesday said trout tested from the river appear to be safe to eat.
The MSI data was compared to national recreational screening levels for long-term chronic exposure. The analysis took into account how a person would contact the river, for how long at each exposure and then how that is repeated over a length of time.
The levels shown in MSI's data reflect EPA screening levels for surface water consumption by an adult or child who intentionally or accidentally ingests 2 liters of water per day, for four days per week, over a 16-week period. The levels are conservative, assuming a person drinks 2 liters of river water every day while swimming or boating four times a week and is exposed to the sediments by camping or living along the river bank for a continuous 64-day period.
"In reality, very few people will experience this level of exposure in any given day, let alone every other day for 16 weeks," the report states.
It also explains that pH dipped as the plume passed in the first 24 hours, but then stabilized to normal levels previously seen in the Animas.
Only manganese exceeded water-quality levels, which is naturally high in the Animas. Many were especially worried about mercury, but that was barely detectable after the plume moved through, and that offers a positive sign to researchers. Still, they urge caution moving forward.
"We don't know exactly how those sediments will respond, where they'll be transported to ... " Bidwell said. "The way we interact with metals is complicated, unlike drinking water where there's a clear path of how we connect with it ... our exposure to the sediments is nowhere near as simple."