The city has dumped more than 215 Olympic-sized swimming pools worth of human waste and storm water into the Ottawa and Rideau rivers so far this year.

More than half of that got dumped on one day back in June, when 324,030 cubic meters of “combined sewer overflow” was released.

It’s a problem the city has been trying to tackle since 2006, but progress has been slow. The Ottawa River Action Plan calls for $195 million to build giant underground vaults to hold sewer water when heavy rain would otherwise trigger overflows. That storage facility was supposed to be finished by 2013 but the city has yet to actually apply for the federal funding it needs for the job.

Ottawans might also remember the rash of beach closures due to high E.coli counts this past summer. In July, when Mayor Jim Watson was campaigning for reelection, he said that getting the underground vaults finished will reduce the number of beach closures from high E.coli. His sentiments are backed up by the city’s latest draft climate change plan and he even had volunteers collecting signatures on a petition supporting the river action plan.

But he’s wrong. An analysis of Ottawa’s rainfall, sewer overflow and beach closure data shows that there is very little relation between sewer overflows and beach closures. When you consider that only one of the city’s four beaches is even downstream of the sewer overflow release points, Watson’s logic appears questionable. City hall did not respond to a numerous requests for comment.

But if it’s not coming from the sewers, where is all the E.coli at Ottawa’s beaches coming from?

Rainwater. Or, more specifically, runoff from heavy rainstorm events. The data shows that on June 24 there was a huge spike in rainfall, and a corresponding spike in E.coli numbers. The rain also triggered the largest sewer overflow event of the summer, but over the next two weeks the Westboro and Mooney’s Bay beaches saw two more equally high spikes in E.coli without the expected spikes in sewer overflows. Even Petrie Island’s beaches, which are downstream from the sewer outlet points, were closed less often than Westboro, Mooney’s Bay and Britannia.

“It’s from human waste, but also birds, dogs and other animal sources. E.coli is also getting into the water in heavy rainfall events from what are called ‘non-point’ sources, which is basically run-off from the land,” said Jesse Vermaire, an expert in water ecology and climate change at Carleton University.

Think of it like this:

Cities are dirty. Streets and sidewalks are covered with grime and dirt, spilled chemicals like windshield washer fluid and gasoline, animal and pet feces. There’s a reason you take your shoes off when you walk in your house.

When it rains in a city, Vermaire explained, the water can’t soak into the ground like it does in a forest or field. All of that filth is washed over the sealed-up parking lots, roads, buildings, and alleys, flushed into the storm drain and right into the river.

When it rains like it did in June, dumping 56 millimeters of rain onto the city in 24 hours, it’s like pressure washing the concrete jungle. And those heavy rain events are likely to be a lot more common. As climate change shifts our weather patterns, “there’s a greater probability of getting larger surface storm events,” Vermaire said.

“The average annual rainfall might not change, but there will be larger one-day rainfalls and longer droughts between rainfalls based on climate change,” he said.

The city has been able to reduce sewage overflow events and volumes since it began working on the problem in 2006. Installation of real time monitoring in 2008 was especially helpful. But even though Mayor Watson likes to tout the river action plan’s expensive holding tanks as a solution to the beach closure problem, the real answer lies in almost the exact opposite direction.

Carleton students and Glebe residents might have noticed the traffic calming sidewalks being extended along Sunnyside Ave. When they’re done, those new sidewalks will also have new gardens adorning them, though they aren’t just for decoration.

“Rain gardens is a much nicer term for them, but they’re really a form of bio-retention,” explains Darlene Conway, who manages the city’s storm water management strategy.

“The ORAP is a huge umbrella project that’s meant to address the sewer overflows, but it doesn’t address the other forms of pollution,” she said.

The gardens are part of a pilot project that’s testing bio-retention as a way to help deal with citywide water runoff. The idea is that the gardens will soak up rainwater that is funneled to them, allowing it to be slowly released over time instead of in a torrent. They also act like filters, collecting particles and some pollutants on site.

“Twenty years ago the thinking was ‘well, we’ve got the water all collected in one place, in our pipes and sewers. Let’s put something at the end of the pipes to treat it,’” Conway said.

“Now we’re starting to see a new approach which is to not centralize it. We’re looking at things like green infrastructure that doesn’t cause water to collect and run off into storm drains or rivers. We’re trying to let it dissipate the way it would have before there were developments and pavement,” she said.

The rain gardens are just one idea. Others include using paving stones instead of asphalt and other forms of “low-impact development” as the city repairs old streets or designs new projects like Lansdowne. The long-term goal is to take advantage of the city’s eventual crumbling to rebuild it in a way that isn’t as environmentally damaging. Essentially, the idea is to slowly make over the concrete jungle into more of a sponge, allowing it to absorb, treat and slowly release water the way a forest or field would.

As for the ORAP and its expensive holding tanks, no one is arguing that dumping raw sewage into the Ottawa River is a good idea.

“It’s extremely important to not be dumping human waste into the Ottawa River, and I think it’s great that they’re investing in this infrastructure. But from an ecosystem standpoint there’s a lot of other stuff ending up in the river as well that we need to deal with,” Vermaire said.