Environmental Protection

Wastewater Tunnel Project Completed in Austin

A ribbon cutting ceremony was held earlier this week to celebrate the completion of Austin’s Downtown Wastewater Tunnel project, which has improved wastewater collection for the central and downtown areas of the city.

In 2001, the City of Austin’s Water Utility awarded the engineering firm Parsons a contract for the Downtown Wastewater Master Plan that progressed to a contract to perform design and construction support services for the tunnel. Parsons completed the design for the Downtown Wastewater Tunnel (DTT) project in 2009. The design phases were completed on time and within budget -- and have been providing the city with underground inspection and construction engineering services for the remainder of this critical project.

“From master planning, through design and to construction completion, we are proud to have worked with the City of Austin’s Water Utility on this important infrastructure project,” said Virginia Grebbien, Parsons Group President. “Parsons applied innovative solutions to address subterranean, surface level, and urban issues in the design and throughout the construction phase of the project, including the use of polymer concrete for constructing the tunnel drop and access manholes and vortex hydraulic drop structures to address odor and corrosion issues.

The DTT project is part of the city’s greater 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. Upon completion of the project, wastewater collection of central and downtown areas of Austin has improved, and also allowed two lift stations to be taken out of service.

The 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 20,000 ft. long (3.9 miles), and it intercepts wastewater flows from main downtown interceptors at five locations with provisions for a sixth future location. The tunnel crosses under Lady Bird Lake three times and varies from 55 to 85 ft. below ground or lake surface.

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