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Aqueduct shutdown expected to begin Nov. 4

 

Last updated 11/1/2019 at 12:47am



Joe Naiman

Village News Correspondent

The repair to the San Diego County Water Authority's Pipeline 4 in Moosa Canyon will require a shutdown of the SDCWA aqueduct which is expected to begin Nov. 4, and the CWA's actions also included a unanimous CWA board vote Oct. 24 to approve a change order in the CWA's contract with Fibrwrap Construction Services, Inc.

The change order increases the contract by $140,409 to create a total contract amount of $1,011,751 while also amending the contract to increase the number of carbon fiber layers.

"The purpose of this is to address the thrust load and the additional pressure," said CWA engineering manager Neena Kuzmich.

The CWA's Second Aqueduct includes Pipelines 3, 4, and 5. Pipelines 3 and 5 provide untreated supply to CWA member agencies while Pipeline 4 distributes treated water to member agency turnouts. Pipeline 3 is a steel pipe 72 inches in diameter, Pipeline 4 is a pre-stressed concrete cylinder pipe (PCCP) 90 inches in diameter, and Pipeline 5 is a PCCP 96 inches in diameter. The pipelines are 40 feet apart from each other at their centers, which translates to 32 to 33 feet apart from each other at their perimeters.

CWA staff observed water discharging from the side slope of Moosa Creek on Aug. 2. When the water was sampled it was identified as treated water, which ruled out groundwater and narrowed the source to Pipeline 4 or the Rainbow Municipal Water District pipeline.

The CWA and Rainbow developed a plan to conduct additional investigations to determine which pipeline was the source of the leak and, on Aug. 6, CWA and Rainbow staff determined that the leak was from Pipeline 4. CWA acting general manager Sandra Kerl declared an emergency the following day.

The emergency declaration, which exempts the CWA from the normal contract procurement process and from California Environmental Quality Act review, required ratification by the CWA board at the next board meeting, and that occurred on a unanimous vote Aug. 22.

The leak is where the pipeline has a 22 degree bend. "That was our problem spot," said Marty Miller, who chairs the CWA's Engineering and Operations Committee and who represents the Vista Irrigation District on the CWA board.

Although the emergency declaration allows the CWA to move forward without the environmental review process, the CWA has been coordinating with the environmental agencies.

The operating pressure within Pipeline 4 at Moosa Canyon exceeds 300 pounds per square inch and a catastrophic failure could create considerable environmental damage as well as damage to Pipelines 3 and 5 and to a Rainbow pipeline in the area.

Kerl worked with two contractors who have previously provided work on the Second Aqueduct. On Sept. 5, J.F. Shea Construction, Inc., was authorized to proceed on the installation and removal of two internal steel bulkheads and the temporary aqueduct pressure relief system near the Red Mountain Reservoir.

Pipeline 4 was shut down on Sept. 9 for the installation of the bulkheads to isolate the pipeline, which allowed for inspection to determine the specific repairs. The bulkheads were installed Sept. 10 and 11, and the pipeline was returned to service Sept. 18 although a second shutdown which is the one scheduled to begin Nov. 4 will be necessary to remove the bulkheads.

The Sept. 11 discovery of sedimentation from Moosa Creek flowing into the pipe led to the direction to install a temporary aqueduct pressure relief system near the Red Mountain Reservoir to provide pressure relief upon resumption of water deliveries.

The pipeline inspection also allowed for the determination of the repair method. Relining an internal section with carbon fiber composite is less invasive than pipeline excavation and replacement, which also would require more time and have more of an environmental impact.

CWA staff provided Fibrwrap with a notice of award on Sept. 13. A unanimous CWA board vote Sept. 26 ratified a $950,000 contract with J.F. Shea for the repair of Pipeline 4 and a contract for $871,342 with Fibrwrap for the carbon fiber relining of Pipeline 4. The action also authorized the continuation of the emergency declaration.

The installation of the temporary aqueduct pressure relief system was completed Sept. 30. The initial Fibrwrap design was based on a preliminary review of the pipeline failure, but CWA staff conducted a forensic analysis which was completed Oct. 2.

"From that forensic analysis we identified that there were some higher thrust forces that need to be addressed," Kuzmich said.

The decision was made to add carbon fiber layers, so the work involves 13 layers of fiber which total approximately half an inch thick. The scope of work also includes the installation of anchor rings at both ends. "This prevents water from getting behind those carbon fiber layers," Kuzmich said.

The steel anchor rings include epoxy coating.

"This goes above and beyond the industry standard for carbon fiber repair," Kuzmich said.

Fibrwrap began pipe preparation on Oct. 3, and the carbon fiber design was finalized Oct. 10. The installation of the carbon fiber material began Oct. 10 and was completed Oct. 21.

The shutdown to remove the bulkheads is expected to last 10days.

Kuzmich noted that Pipeline 3 and Pipeline 5 are also vulnerable to such leaks and that the carbon fiber lining will require subsequent action. "It has a design life of about ten years," she said. "We are developing a more permanent fix for these pipelines."

 

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