Lifespan of water mains unpredictable

Dave Bartlett
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Age only one factor in rash of recent breaks, city officials say

St. John’s city council workers use a backhoe to clear soil from a broken water main on Factory Lane in this file photo. — Photo by Keith Gosse/The Telegram

It may seem like the water mains in St. John’s are bursting at an alarming rate.

But according to the city, breaks at this time of year — when the temperature is fluctuating from mild to freezing and back again — are fairly common.

There have been 18 water main breaks of various levels of severity in the city between Dec. 22, 2011 and last week, when The Telegram sat down with Mayor Dennis O’Keefe, public works director Paul Mackey and engineering director Walt Mills.

“There’s usually a bit of a cluster of breaks in the December, January, February period,” Mackey said.

“It’s got to do with temperature. The ground movement, because of frost, and also the water temperature (which) cools, and that has an effect on the pipes too. It causes shrinking and contraction.”

But weather is only partly to blame. Age is a factor in many parts of the city, where pipes can be a century old.

Sometimes contractors or city crews accidentally rupture mains when they’re working near them, which was the case near Bowring Park in late August when a large part of the city’s west end was without water for a few of days.

“But the majority are just random breaks,” said Mackey.

Based on the statistics the city collects, the number of breaks has gone down in recent years.

“What it shows, is from 1995 up to … 2011, we had a total of 847,” Mackey said.

In an average year, there are between 40 and 60 breaks. However, in 2008 there were only 26, the lowest during the time period. On the other end of the scale, in 2002 there was 92 breaks.

Some are major and cause flooding to nearby homes. Many more are minor and are fixed within hours.

But every time a water main valve has to be shut off to deal with a leak, there is a potential that it can cause other leaks nearby, depending on the condition of the pipes.

“Every time you turn a valve you’re creating potential for something to happen,” Mackey said.

That’s because of the stress the change in pressure can have on the water system. And because some valves are as old as the pipes, some become seized or corroded over time.

That means larger areas of the city have to be shut down and drained before repairs can begin.

“I was really surprised when we had that … Bowring Park break … how (far) back from the actual break we had to go to shut off the flow,” said O’Keefe.

“Sometimes these leaks have been going on for a period of time, and we might not notice them,” added Mackey.

“They might be small leaks and then suddenly let go.”

To combat the unpredictability, the city started a leak detection program in 2003 or 2004.

“That actually found a significant number of leaks when they are at the initial stage, before they became full-blown … water main breaks,” Mackey said.

City crews use acoustic equipment to listen for leaks from above ground.

The city has also started what’s called zone metering to monitor water flow in areas around the city. When flow rates become abnormal, the city goes in and inspects to see if a break has happened.

“At nighttime, flows generally decrease,” said Mills.

He said zone meters have been installed in about 75 per cent of the city, with more added each year.

Another thing the city started to do five or six years ago is what’s called valve exercising.

Valves are inspected and turned to make sure they are working properly, and if not they are repaired.

“We’re a lot more proactive than (we used to be) and part of that was stimulated by studies (on water) conservation,” said O’Keefe.

But Mackey said leaks are part of every water system. The goal is to keep them to a minimum.

Mills pointed out the city has changed the material used in water mains over time.

Before the 1970s, most pipes were cast iron. Then the city switched to less brittle, more flexible ductile iron.

Over the past few years, the city moved to plastic PVC for distribution mains, with pre-stressed concrete pipe for the larger transmission lines.

But no matter the material, the life expectancy of water mains is hard to predict.

“There are so many variables that affect the life of a pipe,” said Mills.

“We’ve got lots of pipes in the ground that are a hundered years old that are functioning fine and we’ve had other places where we’ve had breaks at 20 years or less,” he added.

As an example, there are two 16-inch cast iron pipes in the Merrymeeting Road/Mayor Avenue area that were installed at the same time. While one has had a number of breaks, the other remains in good condition.

As for a strategic plan for replacing older sections of pipe, all three officials agree that’s not feasible in most cases.

Mills said there are some capital works projects to replace tranmission mains on the city’s to-do list. And if the city has to tear up a road for other work, crews take the opportunity to replace older distribution lines.

“(But) it’s a huge tear-up and expense,” said Mackey.

So how does the city budget for repairing water main breaks?

The public works department has a maintenance budget that usually covers the average cost.

But if the repairs go over budget, there’s not much the city can do but find the money.

As O’Keefe pointed out, the city can’t leave people without water.

“It’s got to be done and that’s it,” he said.

“One of the most important things the city does is provide water to its citizens, obviously for potable water purposes but also for fire suppression, so it’s important that water supply be there and (be) reliable,” Mills added.

The cost of replacing aging infrastructure in the city — and water mains are only one example — is one of the reasons why O’Keefe has been speaking out lately about a new fiscal arrangement between municipalities and the province.

He went so far as to suggest at last week’s council meeting that without more money coming from the government, city residents could be looking at a property tax increases of between 200 and 300 per cent in coming years.

O’Keefe said other towns and cities in the province may have to do the same as they struggle to balance budgets while maintaining current services, let alone adding new ones.

dbartlett@thetelegram.com

Geographic location: Bowring Park, Merrymeeting Road

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  • Maury D. Gaston
    January 23, 2012 - 13:45

    Polyethylene encased ductile iron has the combination of strength, flexibility, and corrosion resistance to meet that demanding environment, and its larger-than-nominal inside diameter reduces operating costs.