Documents: Collapsed portal led to build-up of water
FARMINGTON — In 1995, a mine portal into the Gold King Mine collapsed, cutting off access to the mine and, probably, trapping water inside the mine, according to an action and work plan released by the U.S. Environmental Protection Agency Friday night.
The plan was drawn up in May 2015, prior to the EPA beginning work on the abandoned mine that had not had maintenance done on it for more than two decades. The EPA released a cost estimate dated March 2015, but the costs for the project have been redacted.
"Conditions may exist that could result in a blow-out of the blockages and cause a release of large volumes of contaminated mine waters and sediment from inside the mine, which contains concentrated heavy metals," the action and work plan states.
That is exactly what happened on Aug. 5, when workers trying to prevent a blowout caused an estimated 3 million gallons of water to leak out of the mine into the Animas River. The workers were excavating above the old adit — or mine tunnel — when the water began to leak.
The safety plan, also released Friday, instructed crews to find the leak and, if possible, stop it and to try to contain the material.
Work to develop the mine's portal is continuing at the Gold King Mine and is expected to be complete by the end of September, according to a schedule drafted Aug. 11.
Water quality in the Animas River in Silverton, Colo., was already poor prior to the spill. Fish couldn't live in Cement Creek — a tributary feeding the river — and, even 20 miles downstream, the fish populations oin the Animas River were limited due to the presence of mine waste.
From the time the last mine in Silverton was closed in 1991, the water quality had been improving up until 2005, according to documents. But in 2005, water quality began to deteriorate.
That led to the EPA having a plan drafted to remediate the Gold King Mine and the nearby Red and Bonita mines. The plan was finalized earlier this year, and crews began work about a month before the spill took place.
The plan was to direct discharge from the Gold King Mine to a treatment pond at the Red and Bonita mine work site, and to remove the debris covering the adit. Crews would then install a new portal structure and rehabilitate the adit.
If all had gone according to plan, the work would have been complete by the end of the year, and the water from the mine would have discharged into its original drainage, according to the plan.
In addition to releasing the action and work plan, the EPA also released its task order statement of work, dated June 25, 2014.
The task order further elaborates on the portal and adit rehabilitation.
"Measures will be taken to control water and metal precipitate sludge and sediment that are impounded behind any blockage at the portal or in the mine," the order states. "This will include the treatment of surge water discharge as necessary to prevent an uncontrolled release and impact to surface water."
While working underground to clear out the blocked adit, a water pump was to be used to lower the water level, according to the order. The order acknowledges that little was known about the nature of the blockage.
"Underground conditions are uncertain and the amount of blockage is not known," the order states.