In another post I have mentioned Chicago’s TARP system. Like many other cities – including Vancouver – Chicago is drained by so-called combined sewers, that serve the dual purpose of conveying sanitary sewage and storm water. When all goes well the combined flow gets treated at the wastewater plant. But heavy storms can overcome the sewers, which then overflow into neighbouring creeks and bays.
To solve this, Vancouver has decided to separate its sewers. This reduces the overflows, but leaves the storm waters untreated. That’s a shame, because the so-called first flush pushes cigarette butts, waste oil, goose poo, plastic bags, and what-have-you into fish habitat.
Chicago, in contrast, decided to create a system of deep, wide tunnels to receive the excess waters, which are later pumped back to the treatment plants. These are enormous; some of the tunnels are over 10 metres in diameter, and the system, called TARP, can store 8.7 million cubic metres.
TARP, which is what the system is called, has so far saved $180 million worth of flood damage, and the number of CSOs have been reduced by half. Great, but not enough. The city has not only launched an aggressive program of green roofs (to limit runoff) but has also decided to connect the deep tunnels with three large reservoirs. These reservoirs, refitted quarries, increase the storage capacity of the system ten-fold. Two of the reservoirs are now on-line; there has been no CSO since.
Remarkable. But I snickered when I read a sentence from their documentation, one I wish Vancouver would be aware of. It reads:
The most obvious solution, replacing combined sewers with storm and sanitary pipes, was determined to be too costly, disruptive to communities, and unable to provide flood relief.
Ah well. Anyways, take a look: