The U.S. Army Corps of Engineers is defending its claim that the Dakota Access pipeline has no significant environmental impact, but it issued only a brief summary of its court-ordered reassessment while keeping the full analysis confidential.

The delay in releasing the full report, including crucial details about potential oil spills, has incensed the Standing Rock Tribe, whose reservation sits a half-mile downstream from where the pipeline crosses the Missouri River.

The tribe said the Army Corps is stonewalling, and it said it will continue to oppose the pipeline. Meanwhile, oil continues to flow through the pipeline two years after opponents set up a desperate encampment to try to block the project.

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In June 2017, a federal judge ordered the Corps to reassess the potential environmental harm posed by the pipeline, saying it had failed to "adequately consider the impacts of an oil spill on fishing rights, hunting rights, or environmental justice, or the degree to which the pipeline's effects are likely to be highly controversial."

The Corps responded in an Aug. 31 memo saying it sought additional information from Energy Transfer Partners, which owns and operates the Dakota Access pipeline, as well as from Standing Rock and other tribes, but did not find "significant new circumstance[s] or information relevant to environmental concerns."

Tribal leaders blasted the reassessment and could choose to challenge it in court.

"The Army Corps' decision to rubber-stamp its illegal and flawed permit for DAPL will not stand," Mike Faith, Jr., chairman of the Standing Rock Sioux Tribe, said in a statement. "A federal judge declared the DAPL permits to be illegal, and ordered the Corps to take a fresh look at the risks of an oil spill and the impacts to the Tribe and its Treaty rights. That is not what the Army Corps did."

The tribe says it hasn't been able to view the Corps' full reassessment. Instead, the Corps released a two-page memo that mentions a larger analysis of potential environmental impacts, but that report is undergoing a confidentiality review prior to release. The Army Corps and the U.S. Department of Justice did not respond to requests for additional information.

"It's dismaying that they are keeping that confidential, because what they released doesn't tell us anything," Jan Hasselman of Earthjustice, an attorney representing the Standing Rock tribe, said. "We all need to see what's in that [report] before any decisions are made."

Memo Fails to Address Oil Spill Risk

A key omission from the Corps' memo was detailed technical information about a worst case scenario spill from the pipeline into the Missouri River and the risks such a spill would pose to members of the Standing Rock reservation, Hasselman said. The reservation is just downstream from where the pipeline crosses the Missouri River, the tribe's water supply. The tribe says it has struggled to get detailed information about potential spills and spill response plans from Energy Transfer Partners.

The company did not respond to a request for comment.

If the tribe concludes that the Army Corps' recent reassessment of environmental impacts posed by the pipeline was insufficient, and they decide to challenge the findings in court, there is still a chance they could stop the pipeline, though the odds of such an outcome are slim.

"Once the pipeline is constructed and the oil is flowing, it's very difficult for courts to have the stomach to overturn decisions that resulted in that outcome," said Sarah Krakoff, a professor of Native American law at the University of Colorado Law School. "This administration won't last forever and when there is different direction from above to the Army Corps and other agencies, then maybe the decisions about the pipeline can change."

Tribes Are Challenging Other Pipelines, Too

The recent memo by the Army Corps comes amid recent successes and capitulations by other tribes challenging pipelines elsewhere in North America.

On Aug. 30, First Nations in British Columbia won a lawsuit against the Canadian government and the Trans Mountain Pipeline company that halted the proposed $7.4 billion Trans Mountain pipeline expansion, which would ship tar sands crude oil from Alberta to British Columbia. The court determined that the Canadian government's environmental impact and public interest assessment for the project was flawed and failed to consult Indigenous peoples.

On Aug. 31, the Fond du Lac Band of Lake Superior Chippewa in Minnesota signed an agreement with pipeline company Enbridge and accepted an unspecified sum to allow the company to construct its proposed Line 3 pipeline through the tribe's reservation.

The Band was faced with having the pipeline skirt their reservation or pass directly through it, something Indigenous advocates say was a choice between two evils.

Prior to the agreement, the Band, along with other Minnesota tribes, had challenged a favorable environmental assessment of the pipeline by the state's Public Utilities Commission. The Fond du Lac Band dropped its legal challenge to the environmental assessment as part of the agreement, according to Frank Bibeau, legal counsel for Native environmental advocacy group Honor the Earth.

"You shouldn't have to trade your ecosystem to have quality of life and decent infrastructure, and that is basically what tribes are being forced to do," Winona LaDuke, Honor the Earth's Executive Director, said.