North Dakota regulators are filing a complaint against the oil company building the Dakota Access pipeline for failing to disclose the discovery of Native American artifacts in the path of construction.

The allegations mark the state’s first formal action against the corporation and add fuel to the claims of the Standing Rock Sioux tribe, which has long argued that the $3.7bn pipeline threatens sacred lands and indigenous cultural heritage.

The stone cairns, which can sometimes mark burial grounds. Photograph: North Dakota public service commission

Julie Fedorchak, chair of the North Dakota public service commission, told the Guardian that on 17 October, pipeline officials found a group of stone cairns –symbolic rock piles that sometimes mark burial grounds – on a site where construction was planned.



The firm, however, failed to notify the commission, in violation of its permit, and only disclosed the findings 10 days later when government workers inquired about it, she said.

“I was very disappointed,” said Fedorchak. “We found out from our inspectors. Who knows when we would’ve found out?”

The rebuke is significant given that public officials in North Dakota have repeatedly criticized Native American leaders protesting against the pipeline and have gone to great lengths to protect the construction sites from demonstrations. The commission will file a complaint this week and the company could face a maximum fine of $10,000 per day for the 10 days without a disclosure, according to Fedorchak.

Native American protesters, who call themselves “water protectors”, said a reprimand from regulators was too little too late and lamented that the state had consistently failed to work with the tribe to prevent the destruction of sacred burial grounds and historic artifacts.

“They are digging up our sites. They are not following the law,” said LaDonna Brave Bull Allard, a Standing Rock Sioux tribe member and founder of the Sacred Stone camp, which activists formed in the spring to fight the pipeline.

Over the last week, construction of the 1,172-mile pipeline – which would carry 470,000 barrels a day from North Dakota to Illinois – has gotten very close to the Missouri river where the tribe fears it would contaminate the regional drinking water.

Indigenous activists, who have faced Mace, rubber bullets, mass arrests and questionable jail conditions, say the project has already bulldozed sacred grounds.

Energy Transfer Partners, the company behind the pipeline, did not respond to a request for comment on Friday, but a lawyer for the firm claimed in a letter to the commission that the construction crew rerouted around the cairn artifacts and filed a report with the state historic preservation office.

The Dakota Access pipeline construction site. Local tribes fear it will contaminate drinking water. Photograph: Josh Morgan/Reuters

The attorney further claimed that the failure to disclose the findings to the commission was due to the fact that the company was busy coordinating a site visit for public officials.

“What we’re concerned about is transparency,” said Fedorchak.

President Obama recently said the US government was exploring ways to reroute the pipeline, but said he would “let it play out for several more weeks”. Indigenous leaders have urged him to permanently save the native lands and surrounding areas from further destruction.

Cheryl Angel, a Sicangu Lakota tribe member who has been at the Standing Rock camps since April, said she has personally seen what appear to be indigenous artifacts in the line of construction and that she believes the pipeline operators have intentionally hidden discoveries of sacred sites and knowingly destroyed them.

“It’s a tremendous blow to our history. They are trying to erase our existence,” said Angel, 56. “That’s a blatant disregard for our culture. That hurts when someone purposefully tries to erase you as people from … the land we’ve occupied for centuries.”

Allard said she suspected the state might be taking action against the company simply because there is now international attention on the conflict.

“They have no choice now, because the world is watching.”

Given the extent to which the government has allowed the pipeline to rapidly progress, Angel said she did not believe regulators wanted to help preserve artifacts.

“It’s almost as if they are working hand in hand with the oil company to go ahead and let them start drilling.”