[jgroszko]

Also the Chicago Deep Tunnel system is pretty massive

"Phase 1, the creation of 109.4 miles (176.1 km) of drainage tunnels ranging from 9 to 33 feet (2.7 to 10.1 m) in diameter, up to 350 feet (110 m) underground, was adopted in 1972, commenced in 1975, and completed and operational by 2006."

https://en.wikipedia.org/wiki/Tunnel_and_Reservoir_Plan