PG&E starts burying its power lines

WALNUT CREEK – Carved into the earth, a narrow furrow is the only clue that the grasslands of Lime Ridge Open Space will soon return to their original splendor, cleared of dangerous power lines that could ignite nearby subdivisions.

The underground project, costing $3.75 million per mile, represents the start of a 10,000-mile effort by Pacific Gas and Electric to bury state distribution lines to address risk increasing winds and forest fires linked to global warming.

“This is a one-time investment to eliminate virtually all powerline-related ignition hazards, with the added benefit of reducing reliability issues,” said Jamie Martin, who oversees the landfill initiative. from PG&E. “It’s a permanent risk reduction.”

The utility has long resisted calls to bury its power lines because it was too expensive.

But after its equipment was blamed for starting a series of devastating wildfires in Northern California in recent years that have killed dozens of people and destroyed thousands of homes, the company has reversed his position. He filed for bankruptcy in 2019 after facing $30 billion in fines and liability related to the wildfires, and pleaded guilty to 84 counts of manslaughter in the blaze camp of 2018 that destroyed the city of Paradise.

Other fire-prone areas in the Bay Area are also targeted for landfill. Based on an analysis of weather conditions, fire history, tree density, outage data and other factors, priority is given to parts of Santa Rosa, Rossmoor, Pacifica, La Lucas Valley of West Marin and the coastal towns of Pescadero and Davenport.

Only 175 miles will be buried this year, but the project will accelerate. PG&E, the nation’s largest utility, has estimated that about 3,600 miles will be driven between 2022 and 2026. When all 10,000 miles are underground, risk will be reduced by 70-80% in high-pressure districts. fire hazard, Martin said.

There are disadvantages. There is a risk of underground faulting, caused by groundwater contamination, damage to cables during installation, and failure of cable splices and other connections.

And it’s a very expensive approach.

“We are not convinced that landfill offers the greatest reduction for the most effective cost,” said Mark Toney, executive director of TURN, The Utility Reform Network. “And that’s really important, because we’re in an affordability crisis, when it comes to monthly electricity bills. We want PG&E to look at other options. We doubt that taxpayers will end up getting their money’s worth.

But stopgap measures, such as power outages for public safety on windy days, have proven disruptive, abruptly cutting off power to tech-dependent communities. Tree pruning requires constant effort.

Meanwhile, burying wires and cables becomes cheaper and easier. With innovations in tools and techniques, the utility expects the cost to drop to $2.5 million per mile by 2026.

“PG&E is very smart in doing this. It’s a great decision,” said Samuel Ariaratnam, director of the construction engineering program at Arizona State University.

This is a trend all over the United States as climate change causes severe weather events.

“It’s not just a California problem. It’s a national problem,” said geotechnical engineer Brian Dorward of Brierley Associates. “California has wildfires. Florida has hurricanes. The Midwest has tornadoes. All natural disasters wreak havoc on power lines, which are critical infrastructure.

But none offered a project on the scale of PG&E’s new plan. San Diego Gas & Electric, a smaller utility, buried 44% of its distribution lines and 4.4% of its transmission lines. In cities like Manhattan, the lines have been underground for years. Germany and the Netherlands are preparing to put all their lines underground.

Compared to other countries, PG&E has been slow to adopt the solution, said Robert McCullough, a veteran energy consultant in Portland, Ore., and assistant professor of economics at Portland State University.

“California is the most regulated state in the country, with some inertia. He is stiff and slow to react,” he said. “But Pacific Gas & Electric is the model child of rigidity. … He should have fixed everything all the time.

In the East Bay, the new underground route through the windswept chaparral of Lime Ridge will connect the Ygnacio Valley subdivisions to Walnut Creek and Concord. Upon completion, tall distribution towers will fall.

The installation method is simple in the soft sedimentary soil of the region. A bulldozer with a plow blade digs the furrows. Twelve-kilovolt lines are buried nearly a meter underground, deep enough to prevent damage from erosion or animals. The lines, just 1 1/2 inches wide, sit inside 6 inch black PVC conduit, allowing heat to dissipate. A second empty conduit, which serves as a reserve, is next to it.

Then the work crews quickly cover it with soil and moisten it. Sometimes they reopen an area to check the integrity and depth of the conduit.

The process isn’t always so simple in areas where other utilities — gas, cable, fiber optic — are also underground. It requires open trenches, a slower, more traditional approach with a lot more hands-on labor.

But new tools are speeding up the work. A powerful device called a “stone wheel” can cut through clean rock faces with a sharp rotating blade. Another, called an “asphalt zipper,” can open a 1,000-foot-long stretch of road in just an hour; using backhoes and jackhammers, it takes days.

If the drilling needs to be deep or a line needs to pass under a river or road, a technique called “horizontal directional drilling” is a better option, Ariaratnam said. Rather than digging trenches, he uses a machine to drill a precision-guided pilot hole, then pulls a conduit, holding the cable, through the hole. Although more expensive than the open cut, it significantly reduces the time and effort spent on restoration.

Better tracking and steering tools make it possible to do “intersectional drilling,” where two underground holes form a single bore, Dorward said. Drill bits, reamers and hole openers are now specially designed, instead of just homemade.

This quickly extends the length of the route, Dorward said. A single drill can open more than 9,000 feet, he said.

For now, PG&E’s program focuses on burying distribution lines closer to homes, rather than major high-voltage transmission lines, the spokesperson said. Jennifer Robinson. It’s more cost-effective and convenient, she says. Transmission lines conduct more heat, so they must be housed in large concrete conduits, she said.

Transmission lines could be a future project. It is more difficult to bury transmission lines; because they conduct more heat, they must be housed in large concrete ducts, she says. And distribution lines are closer to homes.

Although welcomeDuring the effort, McCullough and others called for greater speed and greater expansion.

“We are at the beginning of global warming, not the end,” he said. “We are going to see an increase in average temperatures and wind speeds in the coming years.”

Comments are closed.