DENVER – The 2015 Gold King Mine spill deposited nearly 540 tons of metals over a 9-hour period into Cement Creek, which feeds into the Animas River, the Environmental Protection Agency said Friday in it final report on the scope and ongoing effects of the spill.
The EPA estimated that roughly one percent of the metals, mostly iron and aluminum, contained in the spill came from the mine, with the rest coming from the waste piles on the hillside below the mine adit and the stream bed of Cement Creek.
The study states “the volume of the GKM release was equivalent to four to seven days of ongoing GKM acid mine drainage,” or “one to two days of high spring runoff.”
But, as indicated in previous tests, the river returned to pre-spill levels.
There have been no reported fish kills or significant impacts on other aquatic life, but the EPA will continue to monitor the waterways impacted by the spill, the agency said Friday in a release.
The study also looked at water quality in the Animas to see if it had returned to pre-event conditions and if the impacts of the spill itself had long-term detrimental ramifications on the river given the history of mining in the region.
Historically, contaminants have settled along the banks of the Animas due to mining in the region, so the river has had higher levels of metals found in the mines that are stirred up during times of high runoff. But the EPA said levels did not noticeably increase as a result of the GKM spill.
“The research supports EPA’s earlier statements that water quality in the affected river system returned to the levels that existed prior to the GKM release and contamination of metals from the release have moved through the river system to Lake Powell,” the release said.
Following Aug. 5, 2015 spill, the concentration of contaminants exceeded water quality standards in multiple locations impacted.
This necessitated the building of an interim water treatment plant at Gladstone that was mandated to operate through November 2016, said Cynthia Peterson, community involvement coordinator for the Bonita Peak Mining District. The EPA concluded a public comment session on Dec. 14 regarding the future of the treatment plant, and will release a final decision by the end of January, Peterson said. But the EPA has a preferred course of action.
“EPA’s preferred plan for the water treatment plant is for its continued operations and to look at additional options in the future as we understand more about the nature and spread of the contamination,” she said.
The agency also is conducting remedial investigation to understand the impact of the 48 sites in the mining district, which was named a Superfund site in September, on river contamination, Peterson said. This represents the first step before clean-up operations can begin.