Cal/OSHA has proposed $212,500 in penalties against two employers — the tunneling contractor and the engineering firm that designed the project — after an April collapse inside an irrigation tunnel under construction near Knights Ferry killed a 35-year-old geologist and seriously injured a second worker. Both companies drew willful-serious, accident-related citations, among the most severe classifications in California’s civil workplace-safety enforcement scheme, according to a news release issued by the Department of Industrial Relations (DIR) on October 15, 2026.

According to DIR, on April 14, 2026, a collapse roughly 200 feet inside the Canyon Tunnel construction project trapped two employees. Twyla Capurro, a 35-year-old geologist, was killed, and a second worker was seriously injured. In a statement issued the day after the incident, the South San Joaquin Irrigation District (SSJID) and Oakdale Irrigation District (OID) described the event as a rock fall, said rescue crews recovered Capurro that evening, and announced that all work on the project had been suspended. The districts’ statement described the second worker’s injuries as minor to moderate, a characterization that differs from DIR’s later description of a serious injury.

DIR describes the project as an irrigation water diversion tunnel more than 12,000 feet long, designed by Provost & Pritchard Engineering Group, Inc. and being built by Drill Tech Drilling & Shoring, Inc. for SSJID. Local reporting by the Oakdale Leader identifies the project as a joint SSJID-OID effort to bypass the districts’ aging Joint Supply Canal, with a cost of more than $80 million split 72 percent to SSJID and 28 percent to OID. Trade press reported that SSJID awarded the construction contract to Drill Tech in July 2025, according to Smart Water Magazine. Capurro was a member of the Provost & Pritchard team, according to the districts’ statement and local press.

Cal/OSHA’s investigation concluded that both employers let work go forward without removing or adequately supporting ground that had already been identified as dangerous, and that both failed to securely support the section of tunnel where employees were working — failures DIR says resulted in the collapse. On September 30, 2026, Cal/OSHA’s Mining and Tunneling Unit issued the citations.

Drill Tech, based in Antioch, faces $95,000 in proposed penalties for one serious accident-related ground control violation and one willful-serious accident-related tunnel support violation. Provost & Pritchard, based in Clovis, faces the larger total, $117,500, for the same two categories of violation plus a serious violation related to training.

The DIR release does not cite specific regulation numbers, but the requirements it describes track California’s Tunnel Safety Orders in Title 8 of the California Code of Regulations. Title 8, § 8440 requires a competent person to inspect the roof, face, walls, and ground support system of underground work areas on initial entry and frequently afterward, and requires that loose or dangerous ground be taken down or adequately supported before any other activity proceeds. Title 8, § 8441 requires that all underground working places be kept securely supported with steel sets, timber, rock bolts, shotcrete, mesh, or similar methods. Title 8, § 8407 requires the person in charge, when an employee is first hired or assigned a new task, to determine the extent of that employee’s experience and instruct the employee on recognizing hazards — including ground control hazards — and the measures needed to eliminate them.

Under Labor Code § 6432, a violation is presumed “serious” when Cal/OSHA shows a realistic possibility that death or serious physical harm could result from the hazard, a presumption the employer may rebut. Willful violations are penalized under Labor Code § 6429, which carries substantially higher per-violation maximums and a mandatory minimum.

Cal/OSHA Chief Debra Lee said in the release that “Deaths and serious injuries from tunnel collapses are entirely preventable,” adding that the agency regularly reminds employers to provide support systems that protect workers from being buried or crushed.

The penalties are proposed, and the violations have not been adjudicated. Employers may appeal a Cal/OSHA citation to the Occupational Safety and Health Appeals Board within 15 working days of receiving it. DIR reports that Provost & Pritchard has appealed; the release does not say whether Drill Tech has done so.

DIR also notes that Cal/OSHA’s Bureau of Investigations is conducting a separate investigation that remains open. Under Labor Code § 6315 and Title 8, § 344.51, the Bureau is the unit within Cal/OSHA that conducts criminal investigations; it must investigate cases involving a workplace death and refer the results to the appropriate prosecutor unless it finds the evidence legally insufficient. DIR has not indicated what, if any, referral may result here.

Cal/OSHA Cites Employers $212,500 for Fatal Tunnel Collapse