Suit alleges Yuba Water is steering investigation into Colgate penstock rupture
A contractor hired to rehabilitate the penstock feeding the New Colgate Powerhouse has accused the Yuba Water Agency of causing February’s catastrophic pipeline rupture and attempting to influence the federally ordered investigation into the failure, according to a lawsuit filed last month.
The complaint, filed June 24 in Yuba Superior Court by Drill Tech-Obayashi Joint Venture, seeks a court declaration that the investigation into the Feb. 13 rupture be conducted impartially. The pipe burst released about 130 million gallons of water, trapped several workers, killed hundreds of juvenile Chinook salmon and damaged the New Colgate Powerhouse. The lawsuit does not seek monetary damages.
The dispute centers not only on what caused the failure, but also on who gets to determine the answer.
The Federal Energy Regulatory Commission directed Yuba Water days after the rupture to retain a fully independent engineering team to conduct a forensic investigation into the failure. Drill Tech-Obayashi alleges Yuba Water is steering that investigation away from examining its own operational decisions while focusing instead on the contractor’s work.
The joint venture — made up of Antioch-based Drill Tech Drilling & Shoring and one of Japan’s “big five” construction firms — was awarded a $76.8 million contract in 2025 to rehabilitate the 5-mile-long tunnel and the mile-long penstock that carries water from New Bullards Bar Reservoir to the powerhouse. The project included replacing sections of the penstock, installing new vent piping and constructing a new concrete thrust block. The system had been taken out of service for months while work was completed.
According to the lawsuit, Yuba Water — not the contractor — was responsible for refilling, or “rewatering,” the penstock after construction. The lawsuit alleges the California Department of Water Resources had previously identified the penstock shutoff valve as needing repair or replacement as part of the project. When the agency began rewatering the pipe, it burst about four days into the process, according to the contractor.
DTO contends, according to court documents, that the agency reintroduced water too quickly, failed to refill the system in controlled segments, used inadequate staffing and failed to properly operate the Colgate Penstock Shutoff Valve during the emergency.
The lawsuit also alleges Yuba Water chose to replace sections of pipe upstream of the failure while leaving in service the one section of 1960s-era steel that ultimately burst. DTO says it was hired to install vent piping, a new concrete foundation and replace portions of the penstock, including the portion that burst, but was not asked to repair or replace the emergency shutoff valve.
After the rupture, the company says in court documents that it was barred from the site until inspectors were allowed back in May, when they observed the shutoff valve in an open position. The lawsuit alleges that had the valve been closed promptly, the amount of water released could have been substantially reduced.
DTO also argues the only welds it performed showed no evidence of failure during post-incident inspections.
The incident is being investigated by outside engineers to determine what went wrong, but the company argues the chosen firm is not impartial. The lawsuit asks the court to broaden the scope of the investigation to ensure it examines all potential causes.
The lawsuit alleges Yuba Water Agency’s lawyers prematurely blamed the company, citing a June 4 letter from the agency’s counsel.
“This correspondence makes clear that Yuba Water intends to hold DTO responsible for the incident,” the suit alleges, “while depriving DTO of the information necessary to conduct its own investigation to defend itself against these allegations.”
Yuba Water disputes the allegations.
The water agency is “committed to an independent, thorough and comprehensive investigation into the root cause of the penstock incident,” Yuba Water Agency spokesperson DeDe Cordell said in a statement.
“We do not agree with the claims in the lawsuit,” Cordell said. “We respect the process of the Independent Forensics Team investigating the incident and will defend it against interference, especially from private parties with an interest in the outcome.”
The civil case remains ongoing, with both parties expected back in court in October.
