What a scale of projects. I have seen the second largest combined stormwater overflow detention tank in Europe in Munich which has the size of two scoccer places. The new CSOs in Chicago is from a different star. One will be ready in one month and the second one will be ready, after 10 years of construction, in 2017.
These two big open reservoirs will serve the City of Chicago and will hopefully prevent the city by beeing flooded by heavy rainfalls. 40-50 storms a year occur. The deep tunnel project releases the normal sewer system and takes all overflows down into the ground. The length is about 150 km. The deapest point are the XXL Pumping Stations. There the water gets pumped up and gets treated.