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Infiltration Reduction Pilot

  • Award acceptance (from left): Catherine Gerali, WERF board chairwoman and district manager of Denver Metro Wastewater Reclamation District; Jim Johnson, SPU lead project engineer; Andy Lukas, VP of Brown and Caldwell; and Marilyn Shepard, Sanipor.
  • Broadview homes in the project area from NW 130th to NW 132nd Streets, from 8th to 12th Avenues NW.

In fall 2013, Seattle Public Utilities (SPU) and their consultant, Brown & Caldwell, received a Water Environment Research Foundation Award for Excellence in Innovation for this pilot project.

In a portion of the 12th Avenue NW sewer basin, SPU completed this 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. Over time, mainlines and side sewers can develop cracks and leaks, which allow groundwater to enter the sewer system.

This project involved 95 percent of homes in the pilot area – 87 Broadview homes in the area from NW 130th to NW 132nd Streets, and from 8th to 12th Avenues NW (see map). The flood grouting of mainlines and residential side sewers occurred in August and September 2011. In January and February 2012, fifty additional maintenance holes that contribute to the 12th Avenue NW sewer system were sealed. The project reduced sewage volumes by 66 percent, and reduced peak flow rates by 41 percent, reducing the chance of future sewage backups.

SPU has monitored sewer flows to determine the effect of flood grouting and may use this method to seal additional sewers in the Broadview area. Flood grouting work was successful in sealing the pipes, and therefore reducing groundwater flows from entering the sewer lines in this pilot area.

How the project was implemented

  • On June 21st, the project team met with residents to introduce workers from Bravo Environmental and to demonstrate their truck-mounted miniature cameras used to survey in the insides of the main sewer lines and side sewers.

SPU hired a consultant to perform a camera inspection of the sewer pipes from the inside, both main sewer lines and residential side sewers. They installed cleanouts in those side sewer lines that didn’t already have them. If side sewer lines needed repairs, SPU completed this work at no cost to the homeowner. Once repairs were completed, the new grouting method was used to seal cracks in the sewer lines.

The grouting was implemented with a two-part, non-toxic chemical process and was completed in sections, from one maintenance hole to another. At each maintenance hole, the lines were temporarily blocked (for no more than one day) and then the chemicals applied.