Case study - San Francisco Public Utilities Commission (SFPUC)


Courtesy of Pure Technologies - a Xylem brand

Service: Sahara Leak Detection
Client: San Francisco Public
Utilities Commission (SFPUC)
Project Date: 2004
Type of Pipelines: Transmission Mains
Diameter: 42 and 54-inch
Pipe Material: Cast Iron
Length: 1.72 miles

The San Francisco Public Utilities Commission (SFPUC) provides water to 2.4 million people in San Francisco, Santa Clara, Alameda and San Mateo counties. It serves 29 wholesale water agencies and delivers approximately 260 million gallons of water per day to its customers through a 280-mile pipeline network.

In 1925 and 1935 SFPUC installed water transmission mains across the Newark Slough, which is now designated as an environmentally sensitive wide tidal waterway. These lines, known as Bay Division Pipelines 1 & 2, and Dumbarton Strait Submarine Transmission Pipelines 1,2 & 3 vary by material construction type and diameter. BDPL1 across Newark Slough has been slip lined.

These pipelines had no previous history of failure, but SFPUC’s engineers knew they needed to validate their integrity. 'Since these lines are underwater, if they were leaking we wouldn’t know it. The leak would simply disappear right into the San Francisco Bay,' explained Jonathan Chow, Principal Engineer of SFPUC’s Water Supply and Treatment Division. 'A leak in this line would have serious environmental consequences, but a failure would be disastrous – and would compromise our ability to meet the demands of our clients.' Accordingly, in October 2004, SFPUC contracted with Pure Technologies to inspect these lines using the Sahara® leak location system.

The inspection posed a number of challenges. As the BDPL1 and BDPL2 pipelines ran along the surface, the ball valves that were to be used to insert the system were 8’4' off of the ground. In addition, as the inspection was to take place in a wildlife refuge, the surrounding vegetation and animal life had to be protected. This meant that the cable drum and winch assembly had to be located approximately 100’ away from the valve chambers. Furthermore, all activities conducted in the field had to meet California Department of Fish & Game, Army Corps of Engineers, and Fish & Wildlife Service permit conditions.

Consequently, Pure Technologies, in conjunction with SFPUC’s engineering team, designed a series of system modifications. A scaffolding system was used to reach the elevated valves. The long-range insertions were carried out by passing Sahara’s umbilical tether, which is disinfected before it enters the main, through a 4' PVC conduit. Additional steps were taken to prevent and contain accidental spills from generators, hydraulic power packs and the chlorinated water used for system disinfection.

Pure Technologies conducted the inspection in the fall of 2004. Analysis of the data determined that no leaks were present, confirming the integrity of the line. Mr. Chow was very pleased with this result. 'SFPUC employs best practices in the management of its water transmission mains. The inspection was cost-effective and the results allow us to allocate funds from our long-term capital improvement program with confidence.'

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