Owner: San Francisco Public Utilities Commission
This four-year project was designed to seismically upgrade the raw water transmission system conveying water from the Lower Crystal Springs Reservoir to the San Andrea’s Reservoir. All marine and underwater work took place in highly sensitive drinking water reservoirs.
Working as a sub-contractor Ballard Marine Construction Commercial Divers utilized both Air and NITROX diving systems at depths exceeding 120ft (37m). The project area (including all construction, staging, and access areas) covers approximately 135 acres and is composed of seven distinct project components running approximately 7.6 miles (12km) across the Peninsula Watershed. Three separate work zones were in operation at times mandating full work barge and dive spreads at each location. This included two hyperbaric chambers on each site as emergency precaution.
Remote Operated Vehicle (ROV) inspections were performed at the southern end of the Lower Crystal Springs Reservoir at the Upper Crystal Springs Dam. Inspection of the underwater work was done using a remotely operated vehicle with underwater video and sonar systems. Utilizing the ROV allowed Ballard operators to provide detailed mapping of the 42” pipe and made possible the capture of the aggregate form work marks from previous repairs. Even though the culvert had a “dogleg” in the path of travel, the ROV was able to document anomalies found in the pipe as well as any new damage or the conditions of the internal ring structure.
Confined space diving in a tunnel to a penetration point 60ft (19m), was completed utilizing a sequentially spaced shoring technique that supported the fractured brick walls of the tunnel. This project was located directly over the San Andrea’s fault zone and damage that was repaired after past major earthquakes was again being brought up to current seismic standards.
Lifting of antiquated large screens was completed using salvage techniques that employed lift bags and staged lifts due to the depths.