Here’s the release from the US Bureau of Reclamation:

The Department of the Interior’s Bureau of Reclamation delivered a report on its Gold King Mine technical evaluation to the Environmental Protection Agency today. EPA requested an independent review to assess the cause of the August 2015 Gold King Mine Blowout near Silverton, Colo. and provide recommendations to prevent future incidents from occurring.

The Bureau of Reclamation’s Technical Service Center in Lakewood, Colo. conducted the independent assessment on behalf of Interior. The TSC provides water resources management-related scientific, applied research, and engineering services. The report was peer reviewed by the U.S. Geological Survey and the U.S. Army Corps of Engineers and produced in accord with Interior’s scientific integrity policy.

The report, entitled ‘Technical Evaluation of the Gold King Mine Incident,’ is available for viewing at http://on.doi.gov/1RdRhD6.

Here’s the executive summary from the report:

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:

1. An understanding that water impounded behind a blocked mine opening can create hydraulic forces similar to a dam.

2. Analysis of potential failure modes.

3. Analysis of downstream consequences if failure were to occur.

4. Engineering considerations that analyze the geologic and hydrologic conditions of the general area.

5. Monitoring to ensure that the structure constructed to close the mine portal continues to perform as intended.

6. 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.

From The Durango Herald (Peter Marcus):

Federal investigators said Thursday that engineering errors by an Environmental Protection Agency-contracted team “led directly” to the August Gold King Mine spill, which could have been prevented.

The much-anticipated 132-page report from the Interior Department following the spill of an estimated 3 million gallons of acidic mining sludge into the Animas River, pointed to miscalculations and poor planning…

The Interior Department was charged with conducting an independent investigation after national and international coverage of the event that turned the Animas River orange, shutting the river for eight days because of initial spikes in heavy metals, including lead, copper and cadmium.

The investigation revealed that the EPA team should have drilled into the mine from above in order to determine the level of the mine pool…

EPA officials said the agency is reviewing the report.

“This report, in combination with the findings of EPA’s internal review of the incident, will help inform EPA’s ongoing efforts to work safely and effectively at mine sites as we carry out our mission to protect human health and the environment,” said Nancy Grantham, an EPA spokeswoman.

As for not drilling into the mine to determine the level of water, Grantham said the team found that “site conditions made it difficult to undertake such drilling.”

The report is careful to point out that while the EPA team caused the incident, there could have been a blowout regardless.

“With the passage of time, the continued sediment buildup would have made the ‘plug’ even less able to transmit seepage flow. Eventually, even if no action had been taken, it may have failed on its own,” the report states.

Investigators also went on to highlight the historical context of the blowout, pointing out that the owners of the neighboring Sunnyside Mine installed bulkheads, increasing wastewater in nearby mines. Groundwater conditions in Cement Creek, a tributary of the Animas River, have also been altered by extensive underground mine workings, the extension of the American Tunnel to the Sunnyside Mine and the plugging of the American Tunnel.

“I, again, want to strongly warn the public and the regulators of the potential for catastrophic future failure of the concrete dams placed in the American Tunnel by the operators of the Sunnyside Mine, which would result in a blowout of many magnitudes greater than the one EPA triggered at the Gold King Mine,” Gold King Mine owner Todd Hennis said in a statement.

Gov. John Hickenlooper, a Democrat, said he is focused on making sure future incidents are prevented, damages are assessed and the EPA makes good on its promise to repair damages and compensate victims.

“It’s what we believed from the beginning, this was preventable. It was a mistake, but it was not malicious,” Hickenlooper said. “The world is not a perfect place.”

One outstanding question is whether the state should file a lawsuit against the EPA. But the governor was cautious, stating: “It’s unclear whether there are sufficient damages to warrant the rather significant cost of a lawsuit. … Lawsuits should be a last resort.”

Republican Attorney General Cynthia Coffman said the report adds a certain emphasis to any conversation on negligence.

“From a legal perspective, this adds an interesting layer to the story because … it does appear the report does establish negligence on behalf of the EPA, and that creates a different question about the nature of the accident,” Coffman said. “There are accidents that would have happened no matter what, and there are accidents that are preventable.”

The report stops short of assigning fault to any individuals, despite prior claims from EPA Administrator Gina McCarthy that it would determine fault and any negligence.

A U.S. Army Corps of Engineers official whose review of the conclusions was included in the report expressed “serious reservations” over the EPA’s failure to explain exactly how its communications broke down and why its officials were so insistent on starting work without more information about the complexities involved.

Richard Olsen, a senior geotechnical engineer with the Corps, also questioned why a change in the EPA field coordinator for Gold King led to an “urgency to start digging” even though another EPA official had expressed some uncertainty about the potential risks.

That second EPA official in July asked for an outside review of the agency’s plans by one of the Bureau of Reclamation engineers involved in Thursday’s report. A meeting between the EPA and the engineer had been scheduled for Aug. 14 – nine days after the blowout.

The technical report on the causes of the Aug. 5 spill has implications across the country, where similar disasters could lurk among the hundreds of thousands of abandoned mines that have yet to be cleaned up. Some estimates put the total cost of containing this mining industry mess at more than $50 billion.

The report says the root causes of the Colorado accident began decades earlier, when mining companies altered the flow of water through a series of interconnected tunnels in the extensively mined Upper Animas River watershed.

From the Associated Press (Matthew Graham) via The Farmington Daily Times:

The spill that fouled rivers in three states would have been avoided had the EPA team checked on water levels inside the Gold King Mine before digging into a collapsed and leaking mine entrance, Interior Department investigators concluded.

The technical report on the causes of the Aug. 5 spill has implications across the United States, where similar disasters could lurk among an estimated hundreds of thousands of abandoned mines that have yet to be cleaned up. The total cost of containing this mining industry mess could top $50 billion, according to government estimates.

The root causes of the Colorado accident began decades ago, when mining companies altered the flow of water through a series of interconnected tunnels in the extensively mined Upper Animas River watershed, the report says.

EPA documents show its officials knew of the potential for a major blowout from the Gold King Minenear Silverton as early as June 2014. After the spill, EPA officials described the blowout as “likely inevitable” because millions of gallons of pressurized water had been bottling up inside the mine.

The Interior report directly refutes that assertion. It says the cleanup team could have used a drill rig to bore into the mine tunnel from above, safely gauging the danger of a blowout and planning the excavation accordingly. Instead, the EPA crew, with the agreement of Colorado mining officials, assumed the mine was only partially inundated.

“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,” according to engineers from Interior’s Bureau of Reclamation, who spent two months evaluating the accident…

Members of Congress seized on the report to slam the government’s handling of the spill. But whereas Republicans such as U.S. Sen. Cory Gardner of Colorado focused their ire on the EPA, U.S. Sen. Michael Bennet, also of Colorado and a Democrat, repeated his call for industry reforms to speed mine cleanups.

Guidelines for cleaning up abandoned mines focus on details such as water sampling and treatment. Yet they have “little appreciation for the engineering complexity,” and require but don’t receive significant expertise, the Interior Department’s 132-page report concluded.

Plugging abandoned or inactive mines has been common industry practice for more than a century. The report lists 31 mines across the U.S. where so-called bulkheads were installed since the 1950s to stem the flow of water into or out of a mine.

With coal mines, monitoring and cleanups are funded in part by a fee companies pay. No such arrangements exist for inoperative hard-rock mines, and that’s a national problem, the report noted.

Given industry opposition to efforts to hold mine owners accountable, the cleanup has been left to a scattering of federal and state agencies, without common standards or even lists of the most problematic mines.

In the wake of the Gold King spill, EPA temporarily halted some work at 10 polluted mining complexes in Montana, California, Colorado and Missouri because of similar conditions.

Abandoned hard-rock underground mines are not subject to the same federal and state safety requirements other mining operations must follow, and “experience indicates that they should be,” the report concluded.

“A collapsed flooded mine is in effect a dam, and failure must be prevented by routine monitoring, maintenance, and in some cases remediation. However, there appears to be a general absence of knowledge of the risks associated with these facilities. A comprehensive identification of sites, evaluation of the potential to fail, and estimation of the likely downstream consequences should failure occur, are good first steps in such an endeavor.”

From The Denver Post (Bruce Finley and Jesse Paul):

Man-made changes in the underground landscape, including installation of bulkhead plugs at the nearby Sunnyside Mine, primed conditions for the 3 million-gallon blowout, according to a 132-page report released by the U.S. Department of Interior.

The Aug. 5 spill above Silverton could have been avoided if the EPA and its contractors used a drill to check wastewater levels inside the mine before digging with heavy machinery to open a clogged portal, the report said…

“Current state of practice”

Tens of thousands of abandoned mines across Colorado and other Western states have yet to be cleaned up. And the federal investigators from Interior’s Bureau of Reclamation found that the conditions that led to the Gold King disaster “are not isolated or unique and in fact are surprisingly prevalent.”

There are no standards for reopening inactive mines, the review found.

However, cleanup workers in 2011 at the adjacent Red and Bonita Mine used a drill to bore into the mine from above and check the level of wastewater in the mine 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 report said.

EPA officials pointed to their internal review blaming “technical challenges, safety, timing and cost” as factors in why the agency failed to drill into the mine to check the level of wastewater. They also blamed “the steepness and instability of slopes” at the mine, citing safety.

The investigation concluded the Gold King disaster “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.”

Colorado Sen. Michael Bennet issued a statement saying “the EPA made unacceptable mistakes and did not have adequate procedures in place.” Bennet said he is working on legislation to shield groups that embark on voluntary cleanups at inactive mines from liability and on “hard rock mining reform” to help clean up mines and reduce the risk to communities.

This image was taken during the peak outflow from the Gold King Mine spill at 10:57 a.m. Aug. 5, 2015. The waste-rock dump can be seen eroding on the right. Federal investigators placed blame for the blowout squarely on engineering errors made by the Environmental Protection Agency’s-contracted company in a 132-page report released Thursday [October 22, 2015]

Gold King Mine entrance after blowout August 2015

Health and environmental officials in San Juan County are evaluating the Animas River after roughly 1 million gallons of mine waste water were released Wednesday. August 6, 2015. (Photo courtesy San Juan Basin Health Department)

Gold King mine spill Animas River August 2015 photo — Nancy Fisher via The Colorado Independent

Gold King mine entrance August 14, 2015 via the Environmental Protection Agency

New settlement ponds at Gold King Mine August 2015