Shimmick Construction, the firm contracted to handle the refurbishment; Shimmick had been cited for serious and willful safety violations on an unrelated job in 2011 by Cal/OSHA but neglected to disclose those violations during the bidding for the Twin Peaks Tunnel job. Muni was also criticized for inadequate notice of service degradation to bus lines during the closure, since buses were pulled off regular routes to substitute for trains, and for the death during the project. During the project, it was discovered that the track ballast was contaminated with toxic heavy metals. Muni had planned to replace the ballast, which degrades over time creating a dust called fines, which can turn to mud when water enters the tunnel. In an effort to save time and avoid the cost of disposal, Muni ordered the ballast to instead be reused, but did not ensure that the contractor followed the proper procedure to thoroughly wash and filter the ballast before it was reused. By November 2020, Muni acknowledged that it had made an "oversight" during the 2018 project and that the ballast was likely to create track stability issues in the Eureka Curve just west of Castro station. Taking advantage of an unscheduled closure of the Muni Metro due to the COVID-19 pandemic, the agency replaced the ballast between November 2020 and February 2021. References External links Silent film by SF real estate company of construction of tunnel (1914-17) Muni Metro Railroad tunnels in California Tunnels in San Francisco Tunnels completed in 1918 1918 establishments in California Castro District, San Francisco Underground rapid transit in the United States