In 2001, engineering firm Parsons Corporation was awarded the contract to perform design and construction support services for the project, while the 6.3 km tunnel was bored by contractor SAK Construction.

The Downtown Wastewater Tunnel (DTT) was constructed with tunnel boring machines and includes 70 ft deep access shafts (30 ft diameter) that were converted to tunnel access manholes. The tunnel is approximately 6.3 km long, and it intercepts wastewater flows from main downtown interceptors at five locations with provisions for a future sixth location. The tunnel crosses under Lady Bird Lake three times and varies from 55 to 85 ft below ground or lake surface.

Parsons Group President Virginia Grebbien said “Parsons applied innovative solutions to address subterranean, surface level, and urban issues in the design and throughout the construction phase of the project.”

“This included the use of polymer concrete for constructing the tunnel drop and access manholes and vortex hydraulic drop structures to address odour and corrosion issues,” Ms Grebbien said.

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The DTT project is part of the city's plan to improve Austin's wastewater system and support sustainability. By reducing current flows in the existing interceptors, the tunnel will make wastewater collection capacity available for future downtown development and allows for greater building and population density.