Two employers were cited for alleged ground support and safety violations after a tunnel collapse killed one worker and seriously injured another.

Cal/OSHA has proposed $212,500 in penalties against two employers following a tunnel collapse near Knights Ferry, California, that killed one worker and seriously injured another.

The April 14, 2026, collapse occurred approximately 200 feet inside the Canyon Tunnel construction project, trapping two workers. Twyla Capurro, a 35-year-old geologist, suffered fatal injuries, while another worker was seriously injured.

According to Cal/OSHA, the employers failed to provide adequate ground support in areas where dangerous ground conditions had been identified.

Provost & Pritchard Engineering Group Inc. designed the more than 12,000-foot-long irrigation water diversion tunnel, and Drill Tech Drilling & Shoring Inc. was constructing it for the South San Joaquin Irrigation District.

Cal/OSHA's Mining and Tunneling Unit issued citations Sept. 30 following an investigation into the collapse.

Drill Tech Drilling & Shoring, 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 Engineering Group, based in Clovis, faces $117,500 in proposed penalties for three violations involving employee training, ground control and tunnel support. The citations include one serious training violation, one serious accident-related violation and one willful-serious accident-related violation.

California's tunnel safety standards require a competent person to inspect underground work areas and ground support systems upon initial entry and frequently afterward. Employers must remove or adequately support dangerous ground before allowing work to proceed and ensure workers receive appropriate hazard recognition training.

Cal/OSHA Chief Debra Lee emphasized the importance of proper tunnel support and safety measures to prevent workers from being buried or crushed during a collapse.

Provost & Pritchard has appealed its citations. Cal/OSHA's Bureau of Investigations is conducting a separate, ongoing investigation.

• Friday New Product Roundup: October 16

  This week's products include cut-resistant apparel, carbon-toe work boots, pallet rack repair kits, an automated compressed air control and a weatherproof cable enclosure. Read Now

• Workplace Noise Can Affect More Than Your Hearing

  Long-term exposure to hazardous noise can affect worker safety, overall health and quality of life, making consistent hearing protection essential. Read Now

• Why Hands-On Training Still Matters in a Digital Age

  VR, AR and AI can expand training opportunities, but physical practice remains essential when workers must handle equipment, coordinate with teams and perform correctly in high-risk situations. Read Now

• The Heat Stress Standard and the Employer's Decision Dilemma

  With OSHA's proposed heat rule unfinished but enforcement expanding, the metric an employer chooses to trigger protective action — Heat Index or wet bulb globe temperature — may matter more than the regulation itself. Read Now

• Navigating Electrical Safety’s Gray Areas

  Electrical safety standards provide a framework, but real-world work doesn't always offer clear-cut choices. Five common gray areas show why understanding the hazard, the task and the worker’s qualifications matter when the right decision is not immediately obvious. Read Now

• The Keys to a Successful Smart PPE Rollout

  A rushed rollout produces resistance. A focused pilot and transparency on goals produce a program workers trust. Read Now