Conference Agenda

Many US cities have aging sewer infrastructure that was built prior to environmental regulations and the development of modern urban transportation networks and associated population growth. As a result, many pipes were built in ravines, streams, and low-lying areas that were subsequently filled and built upon. As these systems age with existing challenging maintenance access, now is the time to evaluate and build more resilient sewer systems that reduce environmental, maintenance, and public safety risk. This presentation will discuss the challenges and benefits of simplifying an aging sewer network by abandoning part of an urban sewer system and reversing the flow of an existing sewer pipe.

The City of Portland identified several thousand feet of combined sewer pipe in north Portland for rehabilitation due to mortality risk, hydraulic capacity risk, and operation and maintenance risk. Some of these sewers are located 20-50 feet below ground in an urban park crossing arterials, highways and abandoned rail. Results from an alternatives analysis proved the hydraulic feasibility of abandoning most of the difficult to access pipes within the park and reconstructing the upstream pipe to reverse the direction of flow within the City’s right-of-way. This creative solution avoids significant community disruption, reduces interagency coordination, and provides better access for future maintenance.

Reconnecting service laterals and catch basins to the reversed mainline presented the biggest challenge to flow reversal. In some sections, the proposed invert elevation is as much as 10 feet above the existing invert elevation. Additional topographic survey and potholing was needed to confirm the feasibility of reversing flow without pumping. Despite the complexities of flow reversal, this solution offered an overall benefit to the City of Portland and rate payers by simplifying maintenance and reducing the overall risk within the system.

King County’s Mercer and Enatai Interceptors were built in the 1960s and extend over 14,000 feet from northern Mercer Island into the Enatai neighborhood of Bellevue, Washington. The interceptors receive flows from North Mercer Pump Station, as well as the City of Mercer Island and City of Bellevue sewer systems. Some parts of the system are reaching the end of their useful lives, and future peak flows are projected to soon exceed the system’s capacity.

The new $58 million Mercer Enatai project includes two upgraded pump stations and a 4-mile sewer alignment that passes underneath residential streets, a major arterial, a regional bicycle and pedestrian trail, a navigable waterway, the Enatai hillside, a swim beach and park, and an environmentally-sensitive wetland. The numerous and varied stakeholders needed to be appropriately engaged with the right information at the right time, and in a way that is meaningful for each stakeholder group.

To uphold King County’s goal of being a good neighbor, the project team worked collaboratively, utilizing traditional outreach methods such as open houses, fliers, community events, and small group meetings. The team also used less common methods such as “walk and talks,” bike rides, online open houses, digital presentations, and targeted outreach for specific populations. The Covid-19 pandemic required a quick shift to virtual engagement.

This presentation will review the entire toolbox of outreach methods the project team used during the different phases of the project, and share thoughts on the lessons learned, varying degrees of success, and potential future approaches to engage communities on projects from cradle to grave.