The leak monitoring system for the Dakota Access pipeline could allow nearly 12,000 barrels of oil per day to spill out of the pipeline undetected, according to a 313-page report from the Standing Rock Sioux Tribe to the U.S. Army Corps of Engineers.

The pipeline’s full flow rate is 600,000 barrels per day, according to a report compiled by the tribe and outside experts, and the detection system can’t detect leaks below 2% of that capacity.

In the report, “the tribe challenged the adequacy of leak detection technology used by pipeline company Energy Transfer Partners,” InsideClimate News reports. “The tribe also questioned the company’s worst-case spill estimate and faulted Energy Transfer Partners for failing to provide a detailed emergency response plan to the tribe showing how the company would respond to an oil spill.”

“It’s an ominous threat every day that we live with on Standing Rock, not even knowing if the pipeline is leaking,” said Water Resources Director Doug Crow Ghost. “Right now, there are 18 inches of ice over the Missouri River, and we can’t sample the water to look for hydrocarbons. We’re sitting blind.”

The tribe also questions the worst-case spill scenario in Energy Transfer Partners’ permit application.

“ETP estimates that 12,500 barrels of oil would be the worst-case scenario, but that is based on a nine-minute shutdown time,” said Standing Rock Chair Mike Faith. “By looking at prior spills, we know the true shutdown time is hours, and can even take days.”

Yet Crow Ghost says the company and the Army Corps have yet to even provide the tribe with an unredacted copy of the emergency plan. “They have failed to send us any adequate documentation to help us prepare for when the pipeline breaks underneath the Missouri River,” he said, even though “we are minutes, if not seconds, south of where the pipeline is.”