PG&E Phase I pipeline pull took 18 hours to place 6,400 ft of pipe.

Work started last month on the second stage of Pacific Gas & Electric's effort to place a new natural gas transmission line around and beneath a flood-prone area in California's Sacramento-San Joaquin Delta. The $56.9-million Line 57C Reliability Project calls for a new 6.4-mile, 24-in., high-pressure line placed 100 ft below the fragile delta's rivers and levees. The steel pipeline is being placed at least 2,000 ft from aging levees to protect it from catastrophic events, such as levee failure or breach scour.

Scheduled for commissioning in November, the new pipeline will connect PG&E's McDonald Island gas storage field, about 10 miles west of Stockton, with an existing natural gas transmission pipeline network east of Brentwood. The connection currently depends upon a 19-mile pipeline, L-57B, built in 1974 and installed just a few feet below ground level using open-cut construction techniques. It travels directly under the levees and rivers and crosses the site of what used to be Mildred Island, before a 1983 levee breach submerged the below-sea-level island. The pipeline was not damaged.

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PG&E New route skirts fragile levees and burrows beneath rivers.

The McDonald Island facility is the largest of PG&E's three underground natural-gas storage facilities. The utility uses the summer months to inject natural gas into the storage caverns under the island for use during the winter when demand is high. The stored natural gas can meet 25 to 30% of the utility's demand in the winter, about 30 billion cu ft. But if something devastating happened to the L-57B pipeline, more than 4.2 million customers in the northern and central regions of the state would be affected. The San Francisco-based utility would not be able to use stored reserves, accumulated when prices are low, and would have to purchase gas on the market for much higher prices. Costs would be passed on to customers. "We estimate that if the current pipeline was wiped out the impact on the local economy would be anywhere from $200 million to $1 billion," says utility spokeswoman Jennifer Ramp. Repairs to the pipeline could take two months or longer during flood season.

"There have been levee breaches in the past, and while our pipelines were not affected, those events made us think, 'We need some new technology, because our pipelines are running through levees 100 or more years old,'" says Ramp. When L-57C is completed this fall, PG&E will use both pipelines for transmission, she adds.

PG&E Hercules rig has a pulling capacity of 1.2 million lb.

PG&E started planning the project nearly a decade ago. The utility announced two years ago that a new pipeline would be constructed following completion of the permitting and design processes. The first phase was completed in June, when crews from primary contractor Trigon EPC, Lakewood, Colo., pulled through 6,400 ft of pipeline from McDonald Island under Empire Cut River to the Lower Jones Tract. From there they will pull the second length of pipeline, which is 6,000 ft long, under the Middle River to Bacon Island. The final underwater river crossing will run under Old River, from Bacon Island to Palm Tract; at 6,800 ft, that will be the longest section of the pipeline. According to PG&E, the first and second stages of the project will be the longest 24-in.-dia pipeline pulls ever conducted on the West Coast.

Horizontal direction drilling specialist Michels Directional Crossings, a division of utility contractor Michels Corp., Brownsville, Wis., is responsible for boring the 36-in.-dia tunnel that runs for more than a mile, to depths of 100 ft at the three river crossings. The tunnels are filled with grout to prevent collapse during pipeline installation. The grout is pushed out as the pipe is pulled through. The pull should take about 18 hours for each water crossing.

The pre-welded lengths of high-grade (API 5L Grade X-70) steel pipeline will have a maximum operating pressure of 2,160 psig. Michels will pull them with its "Hercules" HDD rigs, which have a pulling capacity of 1.2 million pounds. Ted Foltz, Michels western regional manager who is overseeing the PG&E project for the company, says 350,000 lb of force is required to pull one mile of the pipeline through the borehole. To anchor the equipment for the pulling, Michels crews drove six vertical casings 30 ft deep into the ground. Because each bore for the pipeline is more than one mile in length, it was necessary to create an "intersect pilot hole," according to Foltz. Michels drill rig operators, working from opposite ends of the pipeline tunnel and with computer assistance, guided the drill bits through the borehole until they met.

Foltz says Michels has done similar work around levees by the Mississippi River but adds that working around the delicate levee system in the California delta means being "extra cautious" and avoiding "putting too much pressure down the hole and damaging the levees." Soil conditions, while manageable, so far have not been ideal. "It's a very stiff plate, which became very sticky and hard to break down," says Foltz, adding that the company addressed the problem in the first phase of pulling by "swabbing" the borehole and breaking down large pieces of soil into smaller ones, so that the reamers and pipeline could be pulled through.