In late June, a freakish and powerful "derecho" storm in the Washington, D.C., area knocked out a bunch of power lines and left more than a million homes without electricity for several days (weeks, in some cases). Soon enough, local officials began calling on the local utility, Pepco, to bury its power lines underground in order to avoid such outages.

There's got to be a better way ...  right? (Katherine Frey/The Washington Post)

But right away, as Sommer Mathis of Atlantic Cities explained, they ran into a familiar obstacle: It's expensive to bury power lines in the nation's capital. A 2010 study (pdf) found that the D.C. area could prevent more than 1,000 outages a year by burying all of its overhead lines. But it would cost $5.8 billion, adding $226 to customers' monthly electricity bills for the next 10 years. Even a partial plan that would bury just some of the lines, and eliminate 60 percent of outages, would cost $1.6 billion.

As it turns out, D.C. isn't exceptional in this regard. The U.S. Energy Information Administration has just released a primer on the cost of burying power lines across the country. What's striking is how wildly the costs for underground lines can differ, depending on the area. In some regions, it's almost as cheap to bury lines as it is to string them from poles. In other areas, the cost of underground wires is much, much higher:

On average, EIA found, underground lines can cost five to ten times more to build, per mile, than overhead lines. And that's only construction. Utilities also have to dismantle the overhead wires when making the conversions. What's more, repair costs can be higher for the underground lines — they don't last as long and have to be dug up when they get old or break. The underground lines are also more vulnerable to flooding. But those costs need to be weighed against the (often steep) cost of blackouts. And overhead wires are more vulnerable during storms.

So different cities have made different calls on whether or not to bury lines. The EIA notes that many denser urban areas, like Manhattan, have figure out how to bury lines relatively cheaply—especially in places where construction crews are already digging anyway for new buildings. And some cities are willing to bear the cost: Anaheim, Calif., for one, has decided to bury all its lines for aesthetic reasons, funded by a 4 percent surcharge on customers. But in other places, like parts of Colorado (which has granite bedrock) or parts of Florida (where the water table is higher), the price tag can prove a formidable obstacle.

All told, the Edison Electric Institute estimates (pdf) that some 18 percent of the country's distribution lines are buried. For the transmission system, only about 0.5 percent of lines sit beneath the surface. "Undergrounding an entire power system," says EIA, "is considered cost prohibitive." Instead, most utilities will just try to bury a few key lines.

Yet there are also other options, the EIA notes, from hardening above-ground infrastructure at crucial junctures to "vegetation management" to smart grid technology that reroutes power when lines go down. Burying power lines isn't the only way to respond to a storm — and often it's not even the most effective strategy.