This is a year of big promises for Ottawa, in the underground department. Most older cities have the problem that their sewage is combined. That is, the storm sewers flow into the sanitary system. When there is a big rain, all the 'crap' (literally!) is washed out into the river.
Toronto had that problem, and it contaminated the beaches every year. They are into a big program of separating the two sewage systems. Chicago decided to install the giant TARP system, which uses huge underground chambers to store storm outflow for later processing. Ottawa has decided to go for this method, but it's not as bad for Ottawa, since heavy rains mean heavy river flow.
Anyway, according to the comments, this could all be hot air! I think their little transit tunnel will be nearly impossible, but large rock chambers take that further down the tail of the probability distribution.