Under currents

If the St. Louis power lines damaged by last month’s heavy storms had been underground and not overhead, more than 700,000 people would not have been left in the dark, said Dan Clark, Columbia’s supervising engineer.

The guarantee of increased reliability during heavy storms is one of the reasons Columbia plans to spend millions over the next five years on burying overhead power lines. If voters approve the electric bond issue on Tuesday’s ballot, nearly $6 million will be spent on converting overhead lines on Columbia’s busiest streets and placing underground lines inside conduits in newer areas around town.

Converting power lines from overhead to underground is expensive and time-consuming, and city officials agree that the benefits of burying overhead lines are hard to quantify.

City officials estimate the cost of burying overhead lines to be $1 million per mile, and a project to convert a few city blocks of power lines can take months. Often paired with other construction projects, such as the repair of a water main or installation of a sidewalk, “undergrounding,” as engineers call it, is no small task.

But it’s worth all the time, trouble and expense, city officials say.

“When burying power lines, there may be a higher upfront cost, but you don’t have to deal with damage from storms, for example, and it just looks better,” said Dan Dasho, director of Columbia Water and Light. “The reliability is there. We plan to work on the areas most visible to folks first.”

In his proposed fiscal year 2007 budget, City Manager Bill Watkins included $200,000 for maintenance of existing underground lines and $800,000 for conversion of existing power lines, the same amount budgeted annually since 2002. Also included is $2.2 million to bury the lines along Broadway between Garth Avenue to West Boulevard and an additional $4 million for underground projects on the Business Loop 70.

Columbia’s Electric Distribution Manager Dan Stokes said one advantage to burying power lines is that with all the lines underground, there is no danger of trees falling on them.

“It keeps people out of your backyard because they don’t have to go out there and trim all the time,” he said. “We’re on a three-year rotation with tree trimming. Every three years if there’s a power line somewhere, we’ve got to go by and assess if any trees nearby need to be trimmed.”

Stokes said that while converting existing lines from overhead to underground is at least 10 times more expensive than constructing overhead power lines and requires more initial planning, the aesthetic appeal and reliability gained from burying power lines is the driving force behind the trend.

“If a storm blows through, for example, you’re not going to lose power with underground lines,” he said.

“The City Council had a study done a couple of years ago, and they wanted to know if it was feasible to underground the entire city in 40 years,” Stokes said. “And the consultant came back and said, ‘No, it’s really not.’ And so it is a long, continuous process that really depends on our community and what people want.”

One technique being used in several city projects to bury existing lines is called directional drilling. Used as an alternative to digging a trench or cutting open a road, directional drilling allows workers to dig a mud tunnel using high pressure fluid inside a long, extended drill with a rotating, cutting head. This type of drilling makes it easier to chop up rocks and debris underground in order to make way for the plastic conduit that will hold the power lines. While directional drilling does the least damage to the streets and sidewalks, the city also uses conventional drilling, or digging a trench, Clark said.

“With any undergrounding project in an established neighborhood, you have to be careful,” Clark said. “Many times, those power lines are only inches from the street and from traffic.”

He cited the example from earlier this week when a team working to bury power lines along Providence Road accidentally hit a water main and gas line while drilling, requiring several hours of repair.

“The process takes a long time because we have to be very, very careful,” Clark said.

Not all conversion of power lines is paid for by the city. With new development, the city works with the developer to share the cost, usually providing the equipment in exchange for the initial work.

“We have shared costs, and agreements with developers,” Clark said, citing several examples of developers digging trenches to install the conduit system and the city coming in later with high-voltage linemen to bury the power lines.

“We started burying power lines in 1976 in alleys downtown,” Clark said. “And we’ve been working at it ever since.”

Clark, who has been with the city Columbia since 1982, said the amount of power line conversion work completed by the city has slowly increased since the 1970s.

“We’re doing a substantial amount of (burying power lines) now, and a lot of that will be determined by City Council, some by developers and some by us,” he said.

Stokes said council members and Mayor Darwin Hindman have pushed to get power lines buried.

“In Water and Light, we like it for the reliability reason, but it’s as political an issue as any other,” he said.

Clark estimates that about 15 percent of the city’s power lines are underground, but he said it’s hard to know for sure.

“You see center city, downtown, that’s all underground,” he said. “And then basically every residential subdivision built in the last 30 years (has power lines) underground. A lot of undergrounding happens when the land redevelops.”

Four contractors bid on a project Wednesday to bury power lines along Business Loop 70 from West Boulevard to Parkade.

PAR Electrical Contractors received the contract from the city, offering the lowest bid of $1.3 million to replace about a mile of overhead lines with sections of 200-amp and 600-amp circuit overhead and to install 2,000 feet of water main.

“We’re burying those lines along with a major sidewalk project,” Clark said. He expects the Business Loop 70 project to be completed in May 2007. He said that as soon as that project is completed, residents and developers will be clamoring to be next in line.

“As soon as we finish that, people are going to start to ask, ‘Could you go from Parkade to Garth, and from Garth to Providence, and from Providence to Range Line,’” Clark said. “And so on.”