Pebble Update: Why the Army Corps says Final EIS won't analyze a tailings dam failure

Despite requests from agencies including the Environmental Protection Agency, when the U.S. Army Corps of Engineers releases the Final Environmental Impact Statement for the proposed Pebble Mine, an Army Corps leader says the EIS will not include an analysis of the impacts of a tailings dam failure.

The Pebble Limited Partnership's preferred plan for the mine would include two facilities for storing tailings, which are the waste products left over after the valuable metals are removed. According to the USACE, Pebble's preferred alternative would include an approximately 2,800-acre storage facility with two embankments for bulk tailings. Pyritic tailings, which can create highly acidic conditions, would be stored in a lined facility with three embankments and cover about 1,000 acres.

In its official comments on the Draft EIS submitted last summer, the EPA recommended that the Corps consider a breach scenario, and this Winter the discussion over whether or not to analyze a tailings dam breach intensified during technical meetings between the Army Corps, EPA, State of Alaska, and 10 other agencies and organizations.

"That was one of the issues that was robustly discussed and debated with all of the cooperators," Sheila Newman, deputy chief of the Regulatory Division of the Alaska District Army Corps of Engineers said in a teleconference Thursday.

"There were two main themes running through the conversation. The first would be whether or not under NEPA a worst-case scenario is a requirement," Newman said.

In 1978, eight years after President Richard Nixon signed the National Environmental Policy Act into law, the Council on Environmental Quality issued regulations further guiding agencies on how to implement NEPA. Part of those regulations required federal agencies to address uncertainties with "worst-case analyses." That requirement stood until it was removed in 1986, which marked the only substantive change to the environmental law until the Trump Administration proposed new rules earlier this month.

The Draft EIS described a total embankment breach, although a catastrophic failure, as extremely unlikely and a "worst-case" scenario. In its July comments, the EPA raised concern that "given the occurrence of multiple large-scale tailings dam releases in recent years at modern operating mine facilities, the possibility of a dam breach may not be too remote and speculative."

Although the Army Corps and cooperators conducted a Dam Failure workshop, which identified the most probable dam failure scenarios and eliminated full breaches as probable scenarios, draft meeting notes from technical meetings in November show that the EPA doubled down on its request for the Army Corps to conduct a full breach analysis.

The EPA voiced concern that most dam factors are due to human factors rather than design. The EPA also cited a U.S. Fish & Wildlife decision to require a full breach analysis for a copper mine in Arizona based on public concern.

The Army Corps and cooperating agencies held additional technical meetings on December 16 and January 14 with update teleconferences on December 12, and January 7 and 21.

In the teleconference call with reporters, Newman said that in addition to determining that a tailings dam breach would be a worst-case scenario and NEPA did not require assessing the impacts of it, there was another reason that led the Army Corps to continue with its decision not to assess a tailings dam breach.

"The second theme helped us understand what the tailings dam construction is and how that's different from tailings dams that have breached. That conversation was conducted by experts in the field regarded subaqueous tailings versus thickened tailings. What this applicant is proposing are thickened tailings," Newman said. "The Failure Modes Effects Analysis that was conducted in the Draft EIS by a group of experts including the State of Alaska's dam folks built scenarios based on what was proposed. Those groups of experts felt that they had adequately captured scenarios that have a probability reasonable to pursue. In other words, that those things would not be speculative to analyze. To conduct a breach analysis on something that the applicant has not proposed was unwarranted."

The Final EIS for the Pebble Project is expected to be completed in early June, which a record of decision coming the following Fall.