it is basicially a big hold tank, they are building one in chicago and alot of big cities to handle excess gray water that overwhelms the sewages system. In times of big rainstorms and lets them hold water then process it rather than just dump it in a lake or ocean untreated which is what a lot of cities did and some still do. one of the reason it looks so good is because once they cap and start it, it is almost impossible to fix it there is one in NY that has lasted 90 years so if they want they can build things right the only reason i know is before i quit i worked for parsons one of the biggest pipeline contractors in the world.sorry to chew your ears off