California Department of Industrial Relations | Cal/OSHA has cited two employers $212,500 in penalties following a tunnel collapse near Knights Ferry that killed one worker and seriously injured another. The investigation found that both employers failed to provide adequate ground support to protect employees working in the tunnel.
On 14 April 2026, a collapse 200 feet inside the Canyon Tunnel construction project trapped two employees. Twyla Capurro, a 35-year-old geologist, suffered fatal injuries, while another worker was seriously injured.
The more than 12,000-foot-long irrigation water diversion tunnel was designed by Provost & Pritchard Engineering Group, Inc. and was being constructed by Drill Tech Drilling & Shoring, Inc. for the South San Joaquin Irrigation District.
Cal/OSHA found that both employers allowed work to proceed without removing or adequately supporting identified dangerous ground. They also failed to securely support the tunnel section where employees were working, resulting in the collapse.
Cal/OSHA’s Mining and Tunneling Unit issued the following citations and proposed penalties:
- Drill Tech Drilling and Shoring, Inc., based in Antioch, was cited $95,000 in proposed penalties for one serious accident-related ground control violation and one willful-serious accident-related tunnel support violation
- Provost & Pritchard Engineering Group, Inc., based in Clovis, was cited $117,500 in proposed penalties for one serious training violation, one serious accident-related ground control violation and one willful-serious accident-related tunnel support violation.
California’s tunnel safety standards require underground work areas and ground support systems to be inspected by a competent person upon initial entry and frequently afterward. Dangerous ground must be removed or adequately supported before other activities proceed, and underground workplaces must be securely supported. Employers must also assess employees’ experience and provide instruction on recognizing hazards and the protective measures needed to address them.
Employers have the right to appeal any Cal/OSHA citation and notification of penalty by filing an appeal with the Occupational Safety and Health Appeals Board within 15 working days from the receipt of notification.
In this case Provost and Pritchard Engineering Group, Inc. has appealed the citations.
Cal/OSHA’s Bureau of Investigations is conducting a separate investigation, which remains ongoing.
