Burying power lines: Is it worth the cost?

It sounds so simple: To keep falling tree limbs from knocking out power, you have to bury the lines.

But that's not a cheap solution.

"You can have a lot of storms based on what it would cost to [put power lines] underground," said Jerry Henry, senior adviser to Puget Sound Energy CEO Stephen P. Reynolds.

Except when damage caused by the storm reaches $40 million to $60 million, which is what PSE is projecting the December windstorm will cost the company.

In the wake of what utility officials are calling the worst storm in company history, PSE is trying to determine whether putting more power lines underground — which runs around $1 million per mile but can vary widely — might in some places actually be worth the cost.

Areas covered by PSE bore the brunt of the storm, and the utility is trying to figure out if anything could have reduced the 700,000 outages on its grid.

"We're going to take a look at the entire system," Henry said.

About 50 percent of PSE's 20,000 miles of power lines are underground. That number is about 20 percent for Seattle City Light, mostly in downtown, the University District and First Hill, company spokeswoman Suzanne Hartman said. And about 40 percent of lines in Snohomish County's Public Utility District are underground, spokesman Neil Neroutsos said.

Henry said PSE will take the next year to determine whether the company should be more aggressive in burying existing lines and using other approaches, such as installing more "tree wire," a cable with a coating that makes it more resilient during a storm.

Seattle City Light is also considering whether more of its power lines should be buried, said spokesman Scott Thomsen, who acknowledged the high expense of putting lines underground. The Snohomish County Public Utility District isn't planning any changes, Neroutsos said.

PSE's answers will depend in part on what makes the most economic sense, Henry said.

That's where plans to go underground often hit a brick wall. Nationally, burying existing overhead power lines costs about 10 times more than stringing them from poles. Henry puts the figure at about 15 times the cost of above-ground lines in Washington state, a difference he attributes largely to higher costs of labor, materials and property here.

In Florida and North Carolina, statewide initiatives to bury power lines would have prompted a rate increase of 80 to 125 percent, according to a report by the Edison Electric Institute, an industry trade group.

But in new construction, it's no more expensive to put wires underground, because the ground is being excavated already. Burying wires has become the industry standard over the past 30 years, and most municipalities' comprehensive plans include a requirement for underground wires in new developments.

Some cities, such as Redmond and Bellevue, make an effort to bury overhead wires in every road-improvement project. Distribution lines are required by law to be buried 36 inches underground.

But it's not a panacea.

While practically impervious to windstorms, underground power lines are vulnerable to flooding, corrosion, overheating, and people who accidentally dig them up, which Henry said happens somewhere in the PSE system once every week or so.

"Typically, it just blows a fuse and puts the neighborhood out of power," he said.

Though underground wires fail less often, they are harder to reach for repairs and maintenance, which can mean outages last longer.

Trees uprooted by windstorms also can damage buried wires, and terrain can hinder the burial of wires in the first place.

Underground wires might not have prevented many of last month's outages, some of which were caused by trees falling on transmission lines, Henry said.

Transmission lines are larger-volt lines that carry power from the generation source to distribution wires in neighborhoods. They can't always be buried, and substations they serve need to be above ground so workers can access them.

And then, of course, there's the underground real-estate market.

"It can get very busy under ground, especially in an older city setting like Seattle, where you've got all this stuff established and you're trying to grab any open area that you can," said Stephen Gibbs, project manager for the city of Redmond.

Redmond included burial of utility wires in its most recent road improvement — a widening and culvert-replacement project on Northeast 116th Street. The cost to bury the lines was about $800,000, Gibbs said.

The city's share of burying the wiring worked out to $350 to $400 per foot, Gibbs said. A developer and the utilities paid the rest.

Despite the costs and other caveats, Henry said he's "absolutely convinced" that the future of power lines lies underground. The public will demand it, if only for aesthetic reasons, he said. He also said the technology — including the use of superconductor wires that can carry higher voltage with lower risks — will improve.

There's a worldwide demand for better underground wiring, he said, though the need is not imminent. Overhead lines can last 50 to 75 years or more and fail individually, like parts on an aging car, so it will take years before the ones we've got wear out.

Some people don't want to wait. Each year, three or four groups of homeowners pay PSE to put their wires underground, at a cost to homeowners of several thousand dollars each, while many more who inquire decline to follow through, Henry said.

Bellevue City Councilwoman Connie Marshall said residents of older neighborhoods where power wires are still above-ground are now asking the city to bury them to prevent outages, not just for aesthetic reasons.

If the council decides to retrofit such communities, other projects may have to wait, she said.

"We just have to say we're going to do projects a little bit slower and we're going to do it right."

Not every city wants to pay the price.

When Woodinville city leaders sought to bury wires for aesthetic reasons while widening Little Bear Creek Parkway two years ago, they got hit with sticker shock.

After learning the city's share of the project — which would have also put phone and cable underground — was $800,000, or $2,500 per foot, they opted to forgo burying the lines, public-works director Mick Monken said.

Amy Roe: 206-464-3347 or aroe@seattletimes.com