To accomplish this, city officials formulated a two-pronged strategy: install mechanical devices called inlet restrictor valves and promote downspout disconnection by homeowners citywide. Purchase and installation cost $75 million dollars. This was about a quarter of what traditional sewer system improvements would have cost. Near Chicago, the City of Evanston has installed a similar valve system that has helped reduce basement backup.
A $7.8 million grant from the Federal Emergency Management Agency Hazard Mitigation Grant Program (HMGP) jumpstarted the Chicago project in 1998
Thanks. That explains a lot.