CWA approves acoustic monitoring system for northern pipeline

The San Diego County Water Authority board voted unanimously to award a contract to Pure Technologies US, Inc., for the installation and monitoring support of an acoustic fiberoptic cable monitoring system in Pipelines 4 and 5 between the Metropolitan Water District delivery point in Fallbrook and the Twin Oaks Diversion Structure.

The December 18 authorization awards a contract of up to $2,991,608. The contract is scheduled to expire on September 30, 2011, although subsequent SDCWA action will be required during the Capital Improvement Program budget process to add $511,808 to the Aqueduct Protection Program amount for Fiscal Years 2010 and 2011.

The CWA utilizes a combination of inspection technologies. Acoustic monitoring uses a fiberoptic cable within the interior of the pipeline which senses and records wire break activity on a continual basis. “It’s our early warning system for pre-stressed pipe,” said CWA director of operations and maintenance Gary Eaton.

If an event occurs, it first undergoes a series of acoustic and analog filters to determine whether further analysis is required. The system also notifies staff at the CWA’s operations center in Escondido, who can access the data acquisition computer to view and analyze the event. If a wire break is suspected Aqueduct Protection Program staff are notified, and those staff members will confirm the event as an actual wire break and make a preliminary location assessment. Pure Technologies will confirm the location and undertake further analysis and will then forward the data to the CWA.

The CWA has already approved the installation of 27 miles of acoustic fiberoptic cable in its aqueduct system, which totals 82 1/2 miles of prestressed concrete cylinder pipe. The new contract will add 22 miles of acoustic fiberoptic cable. An additional 24 miles have been re-lined, so the completion of the fiberoptic cable in the northern portions of Pipelines 4 and 5 will leave the CWA with only 9 1/2 miles of vulnerable pipe which will not be monitored.

The data collected at the sites of the new installation will assist CWA staff in calculating the current rate of pipeline decay, which is used to update the relining schedule. Annual reviews of the monitoring and inspection data will be compared to the 2006 pipeline decay index to determine if the pipelines are decaying at the calculated rate. If the pipelines are decaying faster than expected, specific segments will be rehabilitated, replaced, or re-lined. If the decay is slower than expected, the internal inspection frequency and rehabilitation schedule will be adjusted.

Pipeline 4 carries treated water while Pipeline 5 transports untreated water. Pipeline 4 provides 72 percent of the Metropolitan Water District’s treated water to the CWA while Pipeline 5 supplies 64 percent of the total untreated water available from the aqueduct. Neither pipeline north of the diversion structure can be shut down for the extended period of time necessary to complete re-lining until Pipeline 6 is constructed. Pipeline 6, which is expected to carry between 470 and 630 cubic feet per second, has been completed between Lake Skinner and Anza Road in Temecula, but the portion between Anza Road and the diversion structure is currently undergoing a feasibility and alignment study. The uncompleted portion of Pipeline 6 is expected to be needed to handle the CWA’s capacity requirements between 2018 and 2023.

A one-day shutdown of Pipeline 5 north of the diversion structure to allow the remote field eddy current contractor the necessary access to scan the pipe and for Aqueduct Protection Program staff to perform a visual inspection and to cross-check past data is scheduled for January 25, and a one-day shutdown of Pipeline 4 north of the diversion structure for those reasons is scheduled for February 8. CWA staff will work with Pure Technologies to install the acoustic monitoring systems during those shutdowns. The next scheduled shutdowns for those pipelines north of the diversion structure are in 2012 for Pipeline 4 and in 2013 for Pipeline 5.

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