Here is the report from the U.S. Bureau of Reclamation. I have not read it yet - just the Executive Summary, which I have pasted below. Not encouraging.
Download Technical-evaluation-of-the-gold-king-mine
Executive Summary
On the morning of August 5, 2015, mine reclamation activities led by the
U.S. Environmental Protection Agency (EPA) onsite project team triggered an uncontrolled rapid release of approximately 3 million gallons of acid mine water from the Gold King Mine located about 5 miles north of Silverton, Colorado. Commonly referred to as a “mine blowout,” the outflow carried with it iron oxyhydroxide sediments that had deposited inside the mine workings. The iron oxyhydroxide absorbed heavy metals when it formed in the mine, and when released it changed the acid water to a vivid orange-brown color. The blowout eroded soil and rock debris from the mine portal, eroded pyritic rock and soil from the adjoining waste-rock dump, and eroded road-embankment fill from several downstream unpaved road stream crossings. Most of the eroded rock, gravel, and sand were deposited in Cement Creek. As the flow continued downstream, deposition of small amounts of soil particles mixed with orange- brown iron-oxyhydroxide precipitates containing heavy metals continued to occur along the Animas River and San Juan Rivers until the plume reached Lake Powell in Utah on August 14, 2015.
EPA requested an independent technical evaluation of the Gold King Mine incident. The evaluation provided in this report was performed by the Bureau of Reclamation (BOR) and peer reviewed by the U.S. Geological Survey (USGS) and the U.S. Army Corps of Engineers (USACE).
In preparing this report, BOR found that the conditions and actions that led to the Gold King Mine incident are not isolated or unique, and in fact are surprisingly prevalent. The standards of practice for reopening and remediating flooded inactive and abandoned mines are inconsistent from one agency to another. There are various guidelines for this type of work but there is little in actual written requirements that government agencies are required to follow when reopening an abandoned mine.
The uncontrolled release at Gold King Mine was due to a series of events spanning several decades. Groundwater conditions in the upper reaches of Cement Creek have been significantly altered by the establishment of extensive underground mine workings, the extension of the American Tunnel to the Sunnyside Mine, and the subsequent plugging of the American Tunnel. The final events leading to the blowout and uncontrolled release of water occurred due to a combination of an inadequately designed closure of the mine portal in 2009 combined with a misinterpretation of the groundwater conditions when reopening the mine portal in 2014 and 2015.
In attempting to reopen the Gold King Mine, the EPA, in consultation with the Colorado Division of Reclamation, Mining and Safety (DRMS), concluded the adit was partially full of water based on excavations made in 2014 and 2015 into the downstream side of backfill placed at the portal. Adit seepage was observed in the downstream excavations to be emerging at an elevation about 6 feet above the adit floor. It was incorrectly concluded that the water level inside the mine was at a similar elevation, a few feet below the top of the adit roof. This error resulted in development of a plan to open the mine in a manner that appeared to guard against blowout, but instead led directly to the failure.
The collapsed material in the adit and the backfill added in 2009 were derived from the collapsed rock and soil that contained a significant amount of clay. It was not a typical roof collapse comprised of mostly cohesionless broken rock. The clay content contributed to the significant attenuation (head loss) of flow in the collapsed debris and the placed backfill as the mine water flowed through it. Also, deposition of iron-oxyhydroxide sediments inside the mine likely contributed to additional reductions in the seepage flow as the sediment layer grew thicker with the passage of time. Changes in seepage were observed and documented in photographs in both 2014 and 2015, but its implications with respect to attenuation of the flow through the fill were not accounted for.
After the EPA project team concluded that the adit was not full to the top with water, they implemented a plan to open the mine in a manner similar to the one used successfully to reopen the adit at the nearby Red and Bonita Mine in 2011. The plan consisted of excavating the fill to expose the rock crown over the adit but leave the fill below the adit roof in place. Then a steel pipe (“stinger”) would be inserted through the fill and into the mine pool, a pump would be attached, and the water in the mine would be pumped down.
A critical difference between the Gold King plan and that used at the Red and Bonita Mine in 2011 was the use in the latter case of a drill rig to bore into the mine from above and directly determine the level of the mine pool prior to excavating backfill at the portal. Although this was apparently considered at Gold King, it was not done. Had it been done, the plan to open the mine would have been revised, and the blowout would not have occurred.
The incident at Gold King Mine is somewhat emblematic of the current state of practice in abandoned mine remediation. The current state of practice appears to focus attention on the environmental issues. Abandoned mine guidelines and manuals provide detailed guidance on environmental sampling, waste characterization, and water treatment, with little appreciation for the engineering complexity of some abandoned mine projects that often require, but do not receive, a significant level of expertise. In the case of the Gold King incident, as in many others, there was an absence of the following:
An understanding that water impounded behind a blocked mine opening can create hydraulic forces similar to a dam.
Analysis of potential failure modes.
Analysis of downstream consequences if failure were to occur.
Engineering considerations that analyze the geologic and hydrologic conditions of the general area.
Monitoring to ensure that the structure constructed to close the mine portal continues to perform as intended.
An understanding of the groundwater system affecting all the mines in the area and the potential for work on one mine affecting conditions at another.
This evaluation report provides a detailed account of the basis for these findings and recommendations for prudent engineering considerations that EPA (and others) should consider to preclude the occurrence of similar incidents.
It is important to note that although the USACE peer reviewer agreed that the report properly describes the technical causes of the failure, he had serious reservations with the chronology of events internal to EPA from the day of the telephone call to BOR and up to the day of the mine failure. He pointed out that the actual cause of failure is some combination of issues related to EPA internal communications, administrative authorities, and/or a break in the decision path, and that the report was non-specific regarding the source of information concerning EPA documents and interviews with EPA employees and the onsite contractor. The USACE believes that the investigation and report should have described what happened internal within EPA that resulted in the path forward and eventually caused the failure. The report discusses field observations by EPA (and why they continued digging), but does not describe why a change in EPA field coordinators caused the urgency to start digging out the plug rather than wait for BOR technical input as prescribed by the EPA project leader.
The BOR Evaluation Team (evaluation team) believed that it was hired to perform a technical evaluation of the causes of the incident, and was not asked to look into the internal communications of the onsite personnel, or to determine why decisions were made. The evaluation team did not believe it was requested to perform an investigation into a “finding of fault,” and that those separate investigative efforts would be performed by others more suitable to that undertaking.
I won't say my usual 'Enjoy!'
"...BOR found that the conditions and actions that led to the Gold King Mine incident are not isolated or unique, and in fact are surprisingly prevalent." - Executive Summary
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