Successful Procedure: Wastewater Bypass in the Heart of Dallas

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Erin Flanagan

Water/Wastewater Treatment and Reuse Engineer

This article is a preview of a presentation recorded for the Collection Systems Digital Conference presented by the Water Environment Federation.

In downtown Dallas, approximately 40% of the City’s sewer flow passes through a a single 90-inch interceptor structure, which was deteriorating. Because the site is inaccessible to large construction equipment, critical repairs had to take place from within the structure.

To solve this challenge, the City designed a 150-MGD temporary bypass pumping system, routing approximately 2,000 linear feet of multiple pipes were routed over an Interstate 30 bridge, to discharge into a downstream siphon inlet structure. In operation for 34 days in summer 2019, the bypass system protected downtown from sanitary sewer overflows during construction and enabled safe and uninterrupted operation of the City’s collection system while the interceptor structure was shut down.

The temporary bypass pumping system allowed for 24-7, no-flow conditions for in-situ concrete rehabilitation of the interceptor structure. Web-based online monitoring of both bypass pumping wet wells and the siphon inlet structure provided minute-by-minute data on bypass operations in relation to water surface elevations. Operational procedures were developed to keep the gravity interceptors on-line even during peak flow conditions. Failure in the temporary bypass pumping system to meet anticipated flows would have imparted risk on the City for sanitary sewer overflows, risk to human life, customer loss of confidence, public relations interaction, and construction schedule impacts.

Throughout the temporary bypass pumping operations, a direct communications plan allowed the Contractor, City of Dallas, and the Engineer to stay connected and provide an incident-free, successful temporary bypass system and protection of critical infrastructure.

Learn more about this project at the WEF Collection Systems Digital Conference, an online course featuring recorded presentations originally planned for the 2020 Collection Systems Conference. This presentation, which is available to view now, reviews aspects that can be applied to any temporary wastewater bypass pumping system: hydraulics, constraints, redundancy requirements, testing, and operations. Registration is required and PDHs are available.

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Erin Flanagan, PE, BCEE, is a Water/Wastewater Treatment and Reuse Engineer in Dallas.