Water main failure points to larger issue

By Scott Hammers, The Bulletin

A city water main that failed along NE Eighth Street on June 10 spilled tens of thousands of gallons of water and damaged 11 homes, exposing one of the weak points in Bend’s infrastructure — miles of water pipe deemed at risk of breaking.

Developed over the years as the city expanded, Bend’s water system contains more than 473 miles of pipe, about 66 miles of which the city considers at risk of failure. Buried underground, the pipes often show no detectable signs of stress until it’s too late.

The greatest risk comes from city’s oldest pipes, which themselves come in four varieties — steel and galvanized steel, plastic, and cast iron, like the pipe that broke in June. All of these materials enjoyed a period of popularity until they were phased out in favor of ductile iron, used almost exclusively in Bend for more than 30 years. As a result, the highest-risk pipes are largely concentrated in the city’s older neighborhoods.

Tom Hickmann, engineering and infrastructure planning director for the city, said ductile iron pipe has a projected 200- to 300-year lifespan, far better than the types that came before it.

Ductile iron is a different formulation of iron, stronger than other varieties because of the inclusion of graphite that takes on a spherical shape rather than the flake-like graphite found in other irons.

It was only in the 1990s that the last of Bend’s original water pipes, built of wooden staves bound together with wire, were pulled up and replaced, Hickmann said. However, older pipes remain in the parts of town that were largely undeveloped until the shift to ductile iron.

Steel pipe began taking over in the 1930s, Hickmann said, but the pipe produced at the time was often poorly made, held together with a single weld that is prone to failure.

Galvanized steel and cast iron were the city’s materials of choice starting around the 1940s, with the galvanized steel used primarily for small diameter pipes and the cast iron for larger ones.

Plagued by the same weld problems as the nongalvanized variety, the galvanized steel pipes have also had problems with the galvanized coating corroding because of contact with the soil.

While cast iron can be quite durable, it is brittle, and according to Hickmann, poor installation methods mean much of the cast iron around Bend is subject to breaking due to settling in an improperly prepared trench.

“We essentially dug, and we laid the pipe in the trench and backfilled with the same dirt, often with pretty large rock, basalt rock right up against the pipe,” Hickmann said.

Plastic enjoyed a surge in popularity in the 1960s and 1970s, but at the time its vulnerability to breaking down under ultraviolet light wasn’t fully known. Plastic piping stored in the sun before it was buried will deteriorate sooner than might otherwise be expected.

Paul Rheault, the city’s public works director, said replacing all of the cast iron, galvanized steel and steel pipe still in service with ductile iron would cost around $69 million. The plastic pipes in the city system are all on the south end of town, installed by the now-defunct Juniper Utility District. Rheault said the city does not have an estimate of what it might cost to replace these pipes, as it is still considering selling the former Juniper district to the private Roats and Avion water utilities.

The city doesn’t have a formal plan to swap out old pipe for new pipe, but has been replacing what it can when the opportunity presents itself.

Rheault said the city often works in tandem with other utility providers, most recently Cascade Natural Gas. The gas company has been digging trenches in and around downtown Bend to service its lines, he said, giving the city a chance to swap out the mostly galvanized steel waterlines that sit nearby.

Hickmann said though the city knows which types of pipe are most likely to break, identifying a particular section of pipe on the brink of failure is difficult.

Winter is the best time for locating leaks and other signs of imminent failure, Hickmann said, as water usage doesn’t fluctuate day-to-day as it does during the summer months when irrigation drives water demand. Because Central Oregon’s porous soils tend to drain off water as fast as it leaks from a faulty pipe, a sudden surge in water usage in one part of the system can be the best indicator something is wrong.

Hickmann recalled an incident a few years ago, when city crews spent two months trying to pinpoint a suspected leak on Bend’s north end, using microphones to listen to the sound of water flowing through the system.

Despite their efforts, crews were unable to find the source of the leak until a wide sinkhole opened up in the on-ramp to the Bend Parkway near The Riverhouse. The cast iron pipe, 20 to 25 feet below the surface, had washed away much of the soil supporting the road.

Also notable was a 2010 incident on Congress Street near downtown, where a burst pipe caused more than $60,000 in damages to nearby homes.

“Those are the ones that kind of make the news,” Hickmann said. “They’re bigger pipes, and when they fail, they fail in spectacular fashion and they fail with no warning.”

As destructive as a broken water pipe can be, they wouldn’t be so powerful if not for another danger — fire. Fire hydrants will draw 1,000 to 1,500 gallons a minute, he said, while peak demand for a single-family home is only around 5 gallons a minute. If not for the need to provide fire protection, the entire city system could operate using smaller pipes running at lower pressure.

A 2011 study prepared for the city identified the locations around Bend where a pipe break would halt water service for the greatest number of customers, or cause significant drops in water pressure. The study identifies a handful of locations where a single break could cut off water to more than 500 homes, and notes the potential for breaks that could leave heavy users such as St. Charles Bend or Deschutes Brewery without water for a time.

Rheault said that study will be incorporated into an upcoming update of the city’s water master plan, to help prioritize which pipes should be considered for replacement.

With the pipelines from the city’s surface water supply at Bridge Creek and the expanded Outback water treatment plant nearing completion, Rheault said public works may have the funds to launch a more robust effort to replace Bend’s riskiest pipes.

— Reporter: 541-383-0387,


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