A small team recently made initial site visits to Yuba Water's New Colgate Powerhouse in Dobbins to survey damage and begin work to establish safe access to the powerhouse facility following the Feb. 13 penstock rupture on the hillside above. Photo courtesy of Yuba Water Agency

YUBA COUNTY, CA (MPG) - The contractor hired for Yuba Water Agency's Colgate Tunnel and Penstock project has filed a lawsuit against the agency, alleging Yuba Water is attempting to steer the investigation into February's catastrophic penstock rupture away from its own actions and toward the contractor's work.

Drill Tech-Obayashi Joint Venture filed the complaint June 24 in Yuba County Superior Court against the Yuba County Water Agency, also known as Yuba Water Agency.

The complaint seeks declaratory relief, asking the court to clarify the parties' rights and responsibilities regarding the cause of the rupture. It also asks the court, if necessary, to order Yuba Water to expand or modify the scope of its testing plan. The lawsuit does not seek monetary damages at this stage.

"We do not agree with the claims in the lawsuit," said DeDe Cordell, communications manager for Yuba Water Agency. "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. We remain committed to an independent, thorough and comprehensive investigation into the root cause of the penstock incident."

Cordell said Yuba Water expects the Independent Forensics Team to finalize its investigation in September or October.

"We simply ask people to please be patient and wait until that investigation is complete before forming opinions about what happened," Cordell said.

The case stems from the Feb. 13 rupture of Yuba Water's 14-foot-diameter penstock above the New Colgate Powerhouse in Dobbins. The penstock carries water from New Bullards Bar Dam and Reservoir through the Colgate Tunnel to the powerhouse for hydroelectric generation.

According to the complaint and Yuba Water's public updates, the rupture released approximately 400 acre-feet of water down the hillside, causing erosion and damaging the penstock, access road, powerhouse and other property.

In January 2025, Yuba Water awarded Drill Tech-Obayashi a $76.8 million contract for the Colgate Tunnel and Penstock Outage Project. According to the complaint, the project included repairs and improvements to the penstock system, including work related to the Colgate Penstock Shutoff Valve, or CPSV, which is part of the system's emergency closure infrastructure.

The complaint alleges the rupture occurred while the penstock was being returned to service through a process known as "rewatering." Drill Tech-Obayashi claims that process was outside its scope of work and was carried out by Yuba Water or its representatives.

The contractor alleges Yuba Water committed operational errors during rewatering, including introducing water too rapidly, using inadequate personnel and resources, and failing to return water to the penstock in a segmented process to control pressure.

Drill Tech-Obayashi also alleges Yuba Water's proposed destructive testing plan is too narrow and focuses on whether the contractor's work weakened the pipe rather than considering other potential causes. The complaint argues the investigation should also examine issues such as pipe pressure, the original 1960s-era steel, original welds, rewatering procedures and operation of the shutoff valve after the rupture.

According to the complaint, the Federal Energy Regulatory Commission directed Yuba Water after the rupture to facilitate an independent forensic analysis to determine the root cause of the failure. Yuba Water has maintained that the investigation is independent, thorough and comprehensive.

The complaint further alleges Yuba Water has not provided documents Drill Tech-Obayashi requested under the California Public Records Act, including records related to the rewatering plan.

Yuba Water denies the allegations and says the investigation should be allowed to proceed without interference. None of the allegations in the complaint have been proven in court.