In February, the Portland, Ore., Bureau of Maintenance sent a crew in a 55,000-pound truck to investigate a water outage at an apartment complex. “The problem was discovered when the maintenance vehicle fell into a large hole in the street,” says the city's Environmental Services Director Dean Marriott. The incident is a dramatic example of a problem many cities are facing: deteriorating water and sewer lines are developing leaks that suck away the earth surrounding them, creating sinkholes.

Most of the nation's water and sewer lines that are in service were installed shortly after World War II and are approaching the end of their 50-year useful life, according to the Environmental Protection Agency. By 2030, most drinking water utilities will have to spend three and a half times more on pipe replacement than they do today, according to the Denver-based American Water Works Association. The increasingly ailing water infrastructure contributes to costly subsidiary problems, such as sinkholes.

A sinkhole occurs when silt and loose sediment around a pipe are gradually pulled away by water leaking from the pipe, forming a void below the road surface. In Portland, where some of the underground infrastructure is 100 years old, there were water, sewer and storm drain pipes under the road leading to the apartment building, all of which were old enough to have been the source of the problem.

The cost of fixing that 30-foot sinkhole is still being assessed, but another sinkhole that occurred a year ago cost nearly $10 million to repair. “The cost of maintaining the system is growing rapidly as the infrastructure ages,” Marriott says. The city's maintenance spending has increased 27 percent in the last five years. “This is one of those examples where you like to do an asset management program [to enable repairs] before [the pipes] fail, because after they fail the cost is staggeringly higher,” Marriott says.

San Diego is assessing the condition of its 33 miles of corrugated metal pipes, which have caused several sinkholes, says Mohammed Sammak, deputy director of the Streets Division. “We put in a majority of our corrugated metal pipes in the 1950s, 1960s and early ‘70s,” Sammak says. The lifespan of each pipe depends on its thickness, the material used to coat it, and the weight of material on top of it.

San Diego has had to repair three major sinkholes in the past year, Sammak says. On June 6, one opened up in the middle of one of the city's largest intersections. “It happened on a Friday afternoon when traffic was worst,” Sammak says. “It was very, very disruptive.” However, because it was on a public right of way, fixing the sinkhole only cost around $40,000 with city crews doing the work. Another sinkhole that was caused by a city-owned pipe on private property cost nearly $700,000 including litigation fees.

The first phase of the city's pipe assessment, which covers 13 miles of pipes that are in critical condition and on private property, will cost $450,000. The second phase, which will cover the rest of the stormwater network, will cost $1 million, which could be included in the city's 2008 budget.

San Diego public works officials are considering two ways to fix damaged pipes. One is to coat the pipes' interiors with a polymer lining that seals leaks. The other is “slip lining,” in which a smaller pipe is inserted into the existing pipe. Although time consuming and expensive, both approaches avoid digging up the lines, which often is not feasible. “[The polymer coating and slip lining] is what you want to use when you have environmental and spacing constraints,” Sammak says.

While repairing aging water lines is costly, Marriott says it must be done. “Everywhere I go, this is certainly a big topic of discussion,” he says. “There's a huge gap between where we ought to be [in maintaining pipes] and where we are.”