The SFPUC serves drinking water to 2.7 million Bay Area customers through hundreds of miles of pipelines and several tunnels. The SFPUC’s Water Supply and Treatment Division (WSTD) routinely inspects portions of the agency’s pipelines, in which case they isolate and drain the specific section of pipeline to work on it. With the inspection of a major tunnel that is miles long, the access and ventilation for manned inspection is not always a viable option. Enter the Falcon.
In February 2020, WSTD staff planned to inspect the Irvington Tunnel Number 2 (IT2). The 8.5-foot diameter, 3.5-mile-long IT2, parallel to the original Irvington Tunnel Number 1 (IT1), was constructed as part of the $4.8 billion Water System Improvement Program in 2015 and helps connect Sierra Nevada and Alameda Watershed supplies to Bay Area customers. Last year, staff identified potential hydraulic concerns with the tunnel and wanted to investigate it without impacting water supply reliability or wasting a large amount of water. Meet the Falcon.
The Falcon is a high tech remotely operated vehicle (ROV) with advanced video imaging, sonar, and navigation equipment that can inspect the inside of the tunnel while it’s full of water. To protect the safety of the drinking water supply for the 2.7 million customers in the Bay Area, all components of the ROV are thoroughly disinfected prior to launching into tunnel.
Launching an ROV into a water supply tunnel full of water required a lot of preparation in the months prior to the inspection, and great care during the inspection. Crews constructed a temporary wooden ‘dance floor’ or work platform over the shaft where the Falcon entered the tunnel. The floor provided a surface for workers to stand on while removing the shaft lid’s steel support beams and to protect the water deep below from debris during this work. The thoroughly disinfected falcon and its thousands of feet of trailing cable were lowered into the tunnel without incident.
A pilot controlled the Falcon from a mobile control room and operated the Falcon’s four thrusters that adjust the heading of the vehicle at any time. The pilot can stop the Falcon to zoom in for a closer look at a portion of the tunnel when requested. The vehicle used cameras, high definition video, and sonar to carefully document the conditions inside the tunnel. The Falcon took four hours to travel 3.5 miles from the Alameda West Portal in Sunol to the Irvington Portal in Fremont. Preliminary reports indicate no obvious issues inside the tunnel and a final report will summarize and interpret the sonar and imaging data.
“This was truly a team effort,” said Janet Ng, Project Manager. The entire team spanned several SFPUC Divisions and departments, and began the planning and coordination months in advance to account for any issues that may arise. Because of all of this work, the inspection was completed without any issues and the tunnel returned to service in a timely manner.
“There were some nerve-racking moments and long days, but staff stepped up to the challenge and worked through issues together to complete the inspection within the tight shutdown period,” said Ng. “A big thanks to Water Supply and Treatment, the Water Quality Division, Construction Management Bureau, Engineering Management Bureau, and Health and Safety staff for helping to make this happen.”
SFPUC crews have inspected other tunnels in the Hetch Hetchy Regional Water System using this ROV technology, including the Bay Tunnel. The next regularly scheduled inspection of IT2 will be in another 20 years. However, to continue with WSTD’s comprehensive tunnel inspection and maintenance plan, one might see the Falcon or similar ROV’s inside the SFPUC’s other tunnels in the near future.