Seattle Public Utilities

Broadview Sewer & Drainage Improvements

Broadview

We’ll be making sewer and drainage improvements in Broadview neighborhood.

Background

History of the Broadview sewer system

The Broadview sewer system was installed in the 1950s. The many homes and businesses built in the neighborhood since then have added flows to the system, and many have also connected their downspouts and sump pumps directly to the sewers.

Over time, the sewer pipes have also started to deteriorate, allowing groundwater to enter through cracks and other openings. During heavy rains, the amount of water can overwhelm the system and even cause sewage backups into some homes.

As was customary at the time, a separate, piped system to handle stormwater in the neighborhood was never built. Construction and development have increased the amount of paved areas, while many trees have been removed and overall natural surfaces reduced. Where rainwater used to seep into the ground, it now collects on the surface and moves downhill through ditches and culverts.

Program background

Since 2011, Seattle Public Utilities has been working with the community to identify sewer and drainage projects in the areas of Broadview that are most impacted. SPU considered over a dozen options addressing sewer and drainage issues and is pursuing two cost-effective projects. The Dayton Ave N Basin Sewer Project and the 12th Ave NW Basin Drainage Project will focus first on parts of the neighborhood with the highest priority sewer and drainage issues.

When developing and evaluating the preferred sewer and drainage options, SPU considered:

  • Social, financial, and environmental impacts of each option — Examples include construction-related traffic, community preferences, and financial constraints.
  • Overall budget — Proposed projects are constrained by the five-year capital budget and approved rate schedule.
  • Effects downstream — We carefully considered all of Broadview in our planning to ensure proposed projects do no harm to downstream communities or resources.

Early action projects

SPU completed two early action pilot projects in the Broadview neighborhood and has initiated two other small projects to help improve drainage conditions and prevent sewer backups.

  • Infiltration Reduction Pilot (2011) — In a portion of 12th Ave NW sewer basin, SPU completed a pilot project to reduce flows into the sewer system during storms, and therefore reduce the chance of sewer backups into homes. SPU used a new, innovative technology called “flood grouting” to seal the sewer mainlines and side sewers in the pilot area. The project involved 87 Broadview homes in the area from NW 130th to NW 132nd streets, and from 8th to 12th Avenues NW. The project reduced sewage volumes by 66 percent, and reduced peak flow rates by 41 percent. SPU received a Water Environment Research Foundation Award for Excellence in Innovation for this pilot project.
  • Backflow Valve Pilot (2012) — SPU worked with homeowners to install backflow prevention devices to prevent sewer backups into homes. SPU installed 27 backflow valves, and since installation, there has been a reduction in sanitary sewer overflows and claims.
  • NW 120th Outfall Replacement and Drainage Improvement — SPU replaced a failed outfall into Mohlendorph Creek and made stormwater improvements to reduce storm-related flooding.
  • 11th Avenue NW Drainage Improvement Project — SPU improved the sidewalk along 11th Avenue NW to allow for better drainage.