In what its sponsors are calling an engineering marvel, Pacific Gas and Electric Co. will begin Monday the key phase of a $56.9 million underground storage reliability upgrade. It involves what the utility is calling the longest 24-inch-diameter natural gas pipeline pull ever conducted in the West.

A new mile-long pipeline will be forced through a bore hole underneath a river in the flood-prone Sacramento Delta, west of Stockton, CA, to add a second pathway in and out of PG&E’s 100 Bcf capacity McDonald Island underground storage facility.

When the new connecting pipeline is operational in November, McDonald Island will have a badly needed second link to the utility’s backbone transmission pipeline system north of the San Francisco Bay area. In addition, its withdrawal capacity will increase by 100 MMcf/d to 1.7 Bcf/d, according to a utility spokesperson, who stressed that the added pipeline is mostly for reliability — not capacity expansion — reasons.

The 18-hour job, using a 1.2 million-pound pulling capacity to install 6,400 feet of high-pressure gas pipe, is scheduled to begin early Monday using so-called “Hercules” pipe-laying equipment. PG&E is making the work accessible for local news media who want to witness the infrastructure upgrade, which it considers precedent-setting.

Currently, PG&E Line 57B is the storage facility’s only link to the transmission system, running 17 miles between McDonald Island and the backbone system. “While in good operational condition, the existing pipeline crosses an area of the Sacramento River Delta that is the subject of increasing concerns about the stability of the aging Delta levee system,” the PG&E spokesperson said.

The new infrastructure project will provide a second path (Line 57C), running 6.4 miles of 24-inch-diameter pipe along a different route that is expected to enhance reliability. Line 57C is being constructed at a depth of 100 feet below the river crossings and 200 feet from the top of the levee, providing what PG&E considers “maximum protection from any possible event, including levee failure.”

There will be three “pulls,” two of which will be the longest 24-inch-diameter pipe ever handled this way in the West, installing the piping in its bore hole under the Empire Cut River in the California Delta. Levees there have been subjected to increased scrutiny since the failure of New Orleans’ levees in September 2005.

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