Environmentalists who oppose the controversial Dakota Access pipeline have a message for the United States Army Corps of Engineers and the incoming Trump administration: When it comes to pumping oil across North Dakota, past is prologue, and that’s bad news for human health and the environment.

An analysis released Wednesday by the Center for Biological Diversity found that pipelines in North Dakota have spilled crude oil and other hazardous liquids at least 85 times since 1996.

Those spills—an average of four a year—caused more than $40 million in property damage, the center said, citing data from the United States Department of Transportation.

In the largest accident, in July 2013, some 840,000 gallons of crude oil spilled from a pipeline in Tioga, North Dakota, and contaminated a wheat field. The spill, which was not reported for two weeks, cost $17.5 million to clean up.

The analysis was released just days after the Obama administration denied an easement to the Dakota Access pipeline for construction under Lake Oahe, the drinking water supply for the Standing Rock Sioux tribe, which has been on the ground with supporters protesting the pipeline for months.

Instead, the corps will conduct a review of alternate pipeline routes and complete an environmental impact statement for the project.

Randi Spivak, the Center for Biological Diversity’s public lands program director, said the analysis will be submitted to the corps as part of its official review.

“We want the corps to do a full oil-spill risk analysis for every river crossing along the entire route of the project,” Spivak said. “Spills happen, as this analysis shows. It’s not a question of if; it’s a question of when. The reason we did this analysis when we did it is because pipelines commonly spill...and that is why it’s problematic at a river crossing.”

Spivak said her group opposes all new fossil fuel infrastructure projects because of their contribution to climate change, as well as their direct impact on local ecosystems.

Pipelines can fail in a number of ways, including mechanical failure, human error, and subfreezing temperatures that can rupture pipes, connectors, and valves, she said.

Spivak pointed to a study by her group that found that, on average, between 1986 and 2013, one significant oil or gas pipeline incident occurred in the United States every 30 hours, causing nearly $7 billion in damages, more than 2,000 injuries, and more than 500 deaths. A companion time-lapse video documents each significant incident.

As for the Dakota pipeline, “it’s worth repeating it was originally proposed to cross the Missouri River in Bismarck, where residents got the pipeline route changed to a different river crossing that would impact the water supply of the Standing Rock people,” Spivak said.

“The Army Corps is now initiating an environmental impact statement, which is a statement, not a decision,” she said. “But it’s extremely valuable for taking a hard look and evaluating and disclosing environmental harm, [because] there has not been a full analysis of the impact to the Standing Rock water supply or any water crossing.”

Corps officials did not respond to requests for comment. Jo-Ellen Darcy, the U.S. Army’s assistant secretary for civil works, made the decision to deny the easement, even though the corps had recommended that it be granted.

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After meeting with tribal officials, Darcy said it was “clear that there’s more work to do.”

“The best way to complete that work responsibly and expeditiously is to explore alternate routes for the pipeline crossing,” Darcy said in a statement. But her decision, she added, “does not alter the Army’s position that the Corps’ prior reviews and actions have comported with legal requirements.”

One company behind the project, Energy Transfer Partners, did not respond to requests for comment. According to Spivak, it has a “questionable” safety record that includes 29 pipeline safety incidents, in which 9,555 barrels of hazardous liquids were spilled, since 2006.

On Sunday, the company issued a defiant response to the corps’ decision, which it called “just the latest in a series of overt and transparent political actions by an administration which has abandoned the rule of law in favor of currying favor with a narrow and extreme political constituency.”

The Dakota Access pipeline “has done nothing but play by the rules,” the statement said. “[We] fully expect to complete construction of the pipeline without any additional rerouting. Nothing this administration has done today changes that in any way.”

What about the next administration?

Donald Trump once owned a stake in Energy Transfer Partners and wants to see the pipeline completed. His support “has nothing to do with his personal investments and everything to do with promoting policies that benefit all Americans,” the president-elect’s transition team said in a statement.

“Trump will try to overturn this, but it might not be that easy because the laws were not followed,” Spivak said. “They have to take into account that this project is harmful to the climate and the Standing Rock Sioux water supply.”

If that doesn’t happen?

“Court,” Spivak said.