The City of Ottawa talks water quality


Dixon Weir is the General Manager of Environmental Services for the City of Ottawa, responsible for wastewater and drainage, drinking water and solid waste services—although, lately, you might think his job is media relations. Over the summer, Weir has been featured in several media, answering environmental concerns about the state of Ottawa’s sewer systems.

Weir’s demeanour was calm and steady, showing no signs of alarm—unlike some of the local coverage.

At the beginning of August, one of the city’s sewage regulators malfunctioned, sending roughly 6,500 cubic metres of raw sewage into the Ottawa River. Not a pretty picture. Fortunately, the incident didn’t affect public drinking water, only recreational activities. On one hand, accidents happen. On the other, it calls into question the condition of Ottawa’s infrastructure.

“It has drawn a lot of attention,” says Weir. “And it’s important that we have these discussions with the public. Citizens should get the opportunity to understand the situation, because it affects everyone.”

Having said that, Weir also believes people tend to react quickly, without understanding the underlying impacts or consequences. “People became quite alarmed to understand sewage overflow was occurring, but I think it’s important to contextualise it. This isn’t something unique to Ottawa—in fact, there are 80 different municipalities in Ontario alone that have combined sewer systems. It’s inherent in the old design systems that were first constructed in the early 1900s.”

The good news is the City of Ottawa not only knows sewage overflow is a problem, but they have been in the process of fixing it over the past several years. “The City has been upgrading our systems for a while now,” explains Weir. “Overflows aren’t new for us. The discharge of combined sewage overflow has gone on for as long as we have had sewers.”

To put minds at some rest, Ottawa’s existing infrastructure is capturing over 99 per cent of collected sewage and sending it to the treatment plant. Also, the other one per cent only overflows in situations of heavy rainfall. But, as Weir says, “the last cubic metre is the most expensive one.”

What is being done now?
Over the past few years, the City of Ottawa has been planning an aggressive program to address a significant volume of combined sewage overflow. The program involves three technology-based projects, two of which are already under construction.

Before explaining what the plan entails, here is come preliminary information:
• There are 18 locations in Ottawa where an overflow into the river can occur (again, during rainfall).
• Of those 18 sites, there are six that account for 97 per cent of the discharge. One of the six is being addressed with an ongoing sewer separation program.
• The other five sites are the ones in which programs are being implemented (Rideau Canal , Keefer Street, West End regulator, Cathcart and Cave Creek). Because some sites interrelated, they are completed at the same time, hence only three projects.

The diversion programs are based around Real-Time Control (RTC) technology. RTC is a system that can monitor pipe flows and alert the City when pipes have reached maximum capacity, at which point, the excess is diverted elsewhere until the storm is over.

Where is it diverted? Weir explains that in the 1960s, the City built a pipe to intercept sewage from all the old pipes leading to the Ottawa River. The interceptor pipe conveyed the sewage away from the river and on to the treatment plant. The interceptor pipe was constructed with a large enough capacity to be able to convey normal flows, as well as weather flows. Even now, there is still available capacity in that pipe, and that’s where the excess sewage gets temporarily diverted.

“Using RTC technology, we are able to monitor that interceptor pipe and understand what the flow is at all times,” says Weir. “We can then control gates to make sure we have maximized capacity in that interceptor pipe before anything goes to the river. By taking advantage of that space, we can reduce overflow by 65 per cent. In an average rainfall year, we would expect to see about 405,000 cubic metres of combined sewage into the river. But by this time next year, we will have reduced that to 140,000 cubic metres.”

The City is looking forward to commissioning two of the three RTC projects by the early winter.

What will be done in the future?
While a 65-per-cent reduction is significant, Weir recognises that there is still more to be done. The RTC projects are cost-effective and timely solutions that will be very beneficial to the river, but it’s not the final word.

Figuring out the next step was a challenge. As it turns out, righting the water quality of the Ottawa River is more complex than fixing sewer overflows. 

“It’s not just sewage that discharges into the river,” says Weir. “There’s also storm water that carries its own contaminants from running through roads and animal litter. And then there are natural rivers, creeks and streams. For many years, these streams have gone through industrial areas, which also brings a load to the Ottawa River.”

“After our analysis, we were presented with new problems,” he continues. “The question was what we should address first with the limited budget. We needed to figure out what change would bring the biggest benefit.”

The City decided to take advantage of computer modelling that allowed them to mimic how the river behaves, which is a feat when you consider how dynamic the river is. W.F. Baird developed the hydrologic model to see how each discharge mixes with and impacts the river.

“The model allows us to hypothesize what the benefits would be if we spent the money on X or Y,” says Weir. “It becomes a means of comparing capital investments on their benefit to the environment.”

Surprisingly, the model showed that the natural rivers, creeks and streams exerted E. coli. Improving water quality for recreational use meant going up three large rivers and starting there. “It ended being very important for us to address those issues before we started to get into other sewage separation programs,” says Weir. “It wouldn’t have been intuitively obvious had we not done the modeling.”

Coming down the pipe
As far as media attention goes for Weir, the upcoming fall season won’t be much quieter. But it’s a good thing. It’s public consultation time, which gives Weir and his team a chance to show their fellow residents what they have been up to, showcasing RTC technology, as well as their solutions to the E. coli problems from discharging streams.   

“The model has powerful graphics that will allow us to communicate what the benefit will be to the public,” Weir smiles. “They will see what the improvements will mean to the river. It will be an effective public communication tool during the consultation.”

In the meantime, Ottawa citizens swimming at Petrie Island can look forward to a significant improvement to water quality, as far as sewer overflows go. Crisis averted.