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We’ll be making sewer and drainage improvements in Broadview neighborhood.
The Broadview sewer system was installed in the 1950s. The many homes and businesses built in the neighborhood since then have added flow into the system, and many have also connected their downspouts and sump pumps directly to the sewers.
Over time, the sewer pipes have started to deteriorate, allowing groundwater to enter it through cracks and other openings. During heavy rains, the amount of water can overwhelm the system and even cause sewage backups into some homes.
A separate 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, culverts and, in recent years, through rain gardens and roadside swales.
To help us decide what long-term solutions we want to propose, SPU has conducted two pilots in Broadview; the Infiltration Reduction Pilot and the Backflow Valve Pilot.
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. 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.
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
Broadview homes that do not currently meet SPU’s standard level of service for sewer service were eligible for this pilot project. Homeowners were asked to allow SPU to measure the elevation of their basement drains to determine if they were eligible for the installation of a backflow prevention device. These devices help prevent sewer backups into homes.
Twenty-seven households were eligible for backflow valves. Twenty-three households (85%) chose to participate in the pilot project and received installed backflow valves paid for by SPU. Information from this project was used to update SPU’s Broadview sewer system model. SPU contractors then took video footage of candidate homes’ side sewers to examine connections and groundwater issues, decide the best type of device to install, and identify the best location for the devices. SPU installed and paid for devices at eligible homes. Homeowners are responsible for maintaining them.