Collaborative Delivery and Innovation Pass the Test for an At-Risk Wastewater Interceptor Rehabilitation Challenge

The District of Columbia Water and Sewer Authority (DC Water) owns and maintains more than 1,900 mi of sewer that conveys over 300 million gallons per day (MGD) of wastewater to the largest advanced wastewater treatment facility in the world. DC Water has a proactive asset management and preventative maintenance program for inspection and rehabilitation of its sewer assets, including major or large diameter gravity sewer assets. This has led to the identification of high-risk assets for repair before potential catastrophic failure. The East–West Outfall Relief Sewer (EWORS), consisting of twin reinforced concrete rectangular gravity conduits, is a recent example of this management approach that became a collaborative delivery repair project. The upstream junction chamber of the EWORS conveys wastewater from a force main and twin interconnecting branch gravity interceptors, with flow rates up to 700 MGD. The EWORS was identified as a candidate for immediate repair, as its interior outer walls and top slab had severe deterioration, with missing sections of its shared channel midwall. The goal for the project was to return the asset to normal operation in less than 12 months through collaborative delivery between DC Water and its contracted service providers. Phase 1 of the tactical plan focused on diversion of flow with a temporary sheet pile open channel around the EWORS to facilitate the repairs. Phase 2 included evaluation of trenchless rehabilitation alternatives that could provide a long-term repair solution. A variety of repair solutions were evaluated, with the PALTEM Flow Ring system chosen. This innovative system had never been installed in the United States but selected due to its ability to meet the operating conditions, strength of the contractor installing the system, and ability to meet a fast-track schedule. This presentation summarizes the project drivers, timeline and logistical challenges, and an overview of the diversion, rehabilitation, and return to normal operation. It concludes with next step recommendations that prioritize corrosion control strategies for DC Water.