Oil pipeline firm Summit Midstream Partners will pay $35 million in federal and state criminal and civil fines for a 29-million-gallon hydraulic fracking wastewater spill that contaminated land, water and groundwater near Williston, N.D.,for months in 2014-15 before it was halted, said the U.S. Justice Dept. in announcing a settlement with the firm ans affiliates earlier this month.

The event, which affected 30 miles of tributaries of the Missouri River, "is believed to be the largest inland spill in history [that] was visible in photographs taken by satellites, said Lawrence Starfield, acting assistant administrator of the US Environmental Protection Agency Office of Enforcement and Compliance Assurance. EPA and state officials ordered cleanup of contamination caused by the spill, pipeline testing, control room monitoring, and third-party auditing.

The firm, which said it has spent more than $50 million to date on remediation and mitigation, described the fine as “severe under the circumstances.”

In its announcement, Justice said Summit’s "negligence" included design, construction and operation of the Marmon Water Gathering System pipeline, as well as "negligent failure to find and stop the spill after learning of objective signs of a leak,” citing a factual admission signed by the company and filed in court. It said Summit started pipeline operations without meters at both ends of the pipeline to conduct “line balancing” or otherwise having a reliable leak detection system in place.

“Even after the company learned of major drops in pressure and volume ... it negligently continued operations and thus caused millions of additional gallons to be discharged into U.S. waters without learning the cause or pausing operations,” according to a "joint factual statement.

Justice said that Summit "has further admitted that it knowingly did not share all relevant information regarding the volume and duration of the spill and that its reports to federal and state authorities were incomplete and misleading,” according to court documents filed.

“While we consider the overall monetary settlement penalties as severe under the circumstances, particularly given our substantial remediation and mitigation efforts to date, we believe that putting this matter behind us with manageable payment terms over the next six years is in the best interest of all of Summit’s stakeholders and employees,” said Heath Deneke, Summit Midstream president, CEO and chairman, in a statement