The Deep Tunnel System consisted of over 17 miles of Deep Tunnels that were dug 300 feet underground for the purpose of trapping sewer overflows. MMSD felt that this would be the best solution to overflow problems because it would store excess wastewater until it could be treated and then it would convey the wastewater to the treatment plant.
The tunnel took 9 years to build and is a straightforward design concept that combines both horizontal and vertical circular shaft constructions. In the year 2000, the Deep Tunnel System prevented 32 overflows and captured more then 6.6 billion gallons of untreated wastewater.
