In documents of an internal government investigation into the Aug. 5 Gold King Mine spill in Colorado, released Wednesday, Aug. 26, Environmental Protection Agency (EPA) reviewers reported that a work plan accounted for a possible blowout and indicated that large volumes of contaminated mine water could potentially be released.
Investigators determined that the EPA and the Colorado Division of Reclamation, Mining and Safety (DRMS) failed to conduct the proper test, which would have shown an accurate measurement of mine water pressure.
Nevertheless, “experienced professionals” from the EPA and DRMS had determined that since water was able to escape from the blocked mine, there was likely no pressure buildup, states the report.
A cleanup crew hired by the EPA were attempting to remove soil from a solid rock surface above the opening of the mine when the accidental rupture occurred, according to the report.
Starting as a spurt, within three to four minutes, gallons of toxic orange wastewater was gushing out of the mine, eventually polluting the nearby Animas River and rivers in New Mexico and Utah. It took about one hour for peak flooding to subside, eventually emitting 3 million gallons of sludge.
The report notes that conducting the proper test would have been difficult and costly.
Reviewers believe state and federal officials should have drilled a hole further back into the adit (horizontal passage leading into a mine) or have come from above the mine tunnel to get an accurate pressure reading. The complete technique would have involved decanting the wastewater (taking it out of the mine) and treating it, according to Bill Simon, coordinator of Animas River Stakeholder Group, local citizens concerned about water quality problems caused by mining.
“It’s a fairly common occurrence for old draining mines to become blocked because the ground just naturally wants to cave in and the water gets caught up behind the blockage. Then the water can’t get through and eventually the pressure builds,” he said.
Investigators concluded the precautions taken were insufficient. “The inability to obtain an actual measurement of the mine water pressure behind the entrance blockage seems to be a primary issue at this particular site,” the report states. They also should have been alerted to the high pressure from the decrease in flows from the mine opening over the years, which could have indicated a water blockage.
Officials had been working on a nearby troubled mine, the Red and Bonita Mine, where the proper technique was performed finding no pressurization. That mine had been leaking 300 to 500 gallons per minute (gpm).
Excavation of the Red and Bonita mine’s adit proceeded without incident, according to the investigative report. The successful excavation may have boosted the officials’ confidence that wastewater had not flowed down hill into Gold King, but there was reason for concern according to a geologic structure report.
The Red and Bonita leak was caused by a rising water table after workers built a bulkhead (massive plug) to block the tunnel running between Red and Bonita and Gold King. The American Tunnel was constructed in the mid-1900s to assist in draining the Gold King and Red and Bonita Mines, which it effectively did.
By 2002, three bulkheads had been installed, closing off the American Tunnel and the water table began to rise.
“It increased the water table by at least 1,000 feet,” said Simon, “and that puts it [water level] at above the level of the Gold King Mine.” He believes the wastewater flow was able to reach Gold King through natural faults and fissures in the mountains.
A toxic flow continued out of the American Tunnel at 100 gallons per minute and other adits opened up. The Red and Bonita Mine, which previously had no mine water discharge, began spewing 300 gpm. The Gold King Mine increased to 42 gpm, and was at 135 gpm at the time of the Aug. 5 excavation.
In September 2014, EPA officials had planned to install a reinforced bulkhead to stop the flow of contaminated water—containing high levels of metals, especially zinc—from flowing out of Red and Bonita into the Animas River near Silverton, according to a memo seeking permission to open up the entrance of the mine.
In a structural geologic investigation report conducted in 2007, a “major concern” was raised because of a potential unknown groundwater connection between Red and Bonita inner workings and Gold King.
“It is more likely that there are at least a few deep, discrete groundwater-bearing structures that are intersected by both mines,” the report stated, “and therefore it is possible that plugging the [Red and Bonita] adit level could force the local groundwater system to refill and rise high enough along these pathways such that discharge increases at the Gold King Portals.”
Investigators recommended that the Red and Bonita be pressure-tested and the underground workings be investigated to determine the best mitigation approach.
In August 2014, the DMRS reviewed a 1969 plan map and reported that there was no interconnection between the Red and Bonita and Gold King mines.
After the Gold King mine erupted, a mustard colored toxic waste washed into New Mexico’s San Juan River, which is a primary water source for the Navajo Nation and it eventually reached Utah’s Lake Powell—a huge reservoir 300 miles downstream that feeds the Colorado River and supplies water to the Southwest.
All three states issued states of emergency and the rivers were temporarily closed off until water levels were safe. Residents could not drink or bathe in the water and farmers were prevented from irrigating their crops.
In addition to the internal review conducted by EPA, the U.S. Department of the Interior is conducting its own assessment of the Gold King Mine incident. The assessment began on Tuesday, Aug. 18, and a report is expected to be provided to the EPA and the public within 60 days.