September 10, 2010

FOCUS | Sewer and Watermain

Ottawa investing in rehabilitation of water infrastructure

KORKY KOROLUK

correspondent

OTTAWA

Ottawa residents have been using less water for the last several years, and they’re not alone. It’s a trend that has been noted in other municipalities in Canada, says Dixon Weir, general manager of environmental services for the city.

“The declining demand is not particularly unique to Ottawa,” he said in a recent interview. “We met earlier this year with other municipalities across Canada, and they were experiencing a similar situation.”

Large municipalities, in particular, have noticed the trend, he said,

“I was struck by how much ... our trend mirrored that of Toronto’s.”

Contractors looking for work might not agree, but to Weir and the city of Ottawa, the trend is good news.

There was a tremendous growth in infrastructure construction during the years following the Second World War, he said. Much of that infrastructure is now about 60 years old, and the water treatment plants, sewage treatment plants and pumping stations are close to, or beyond their asset-design life, he said. The piping systems might have a slightly longer design life, but they represent most of the value of those systems, “and it is important that we start to pay attention to renewing those, or rehabilitating them where possible.”

“So if we can put off capital expansions, that allows more money to be directed toward renewal and rehabilitation, which is something that all municipalities are facing.”

Weir said water conservation measures involving installation of low-flow toilets, dishwashers and laundry washers are an important reason for the decline in usage. As well, the city has an active program of maintenance and renewal that has helped control the amount of water lost out of the system through leakage as it makes its way to customers through some 2,700 kilometres of water mains.

The result is that “we’re now producing water out of our two water treatment plants at late-1980s volumes,” he said.

At the same time, the flow of water into the city’s sewage treatment plant has held relatively steady as the city’s population has increased.

“We measure a number of different things in the incoming sewage (and) what we have seen is that the solids component arriving at the plant has gone up. But on the liquid side, we haven’t seen that increase,” he said.

That’s because of both lower demand in people’s homes and tightening up the sewage collection system over-all.

The city completed a $95-million expansion of its digester facility at the sewage treatment plant, but with little if any increase in the hydraulic loading at the plant, the planned expansion to handle liquids was postponed.

That delayed project had been expected to cost about $215 million. The delayed project at the Britannia water filtration plant was to have cost about $48 million.

That’s a total of $263 million that has been delayed.

“But those projects haven’t dropped off the page,” Weir said. “We’ll continue to look at them. Our capital program takes a close look within a 10-year horizon, and then looks out 20 and 40 years, but obviously with less precision.”

Another thing the city watches closely is leakage from the water distribution system.

When the problem of leaks first began to get publicity two or three decades ago, it was not uncommon to see estimates of as much as 40 or 50 per cent of water lost. In fact, a recently published estimate of losses from the Montreal system was pegged at 40 per cent.

But Ottawa is “down somewhere in the 15- to 20-per-cent range,” Weir said.

“We do quite a complex analysis to make sure that we’re reducing the amount of water loss, and this year was our fourth consecutive year of reducing those losses.”

There is, however, a point of diminishing returns, so the city is presently examining its program to see if striving for further loss reductions is, in fact, economical.

Another area of concern for the city is the volumes of stormwater as climate change leads to both more and more extreme weather events. What engineers might once have considered to be a 100-year storm, might now be more like a 20-year storm.

That means that engineers will have to consider designing systems with bigger pipes to carry the increased flow.

“That certainly is a concern,” Weir said. “The difficulty has been that while people recognize that there is a trend, there has not yet been a quantification of that trend, or a quantification of what is going to be a 100-year storm, around which we can then start to design things.”

So, since new numbers have not yet been established, the city is “designing things to be a little bit more resilient, and ensuring that we have the redundancy in some of the infrastructure to be able to accommodate an increase over time, or be able to recover more quickly should an extreme weather event occur.”

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