Update on Broadview Sewer and Drainage Improvements

Here is an update on Seattle Public Utilities’ work in Broadview related to the sewer and drainage systems, and Venema and Piper’s Creeks.

Broadview Sewer and Drainage Improvements Project The consultant team for engineering and support services for this project was selected and has begun working with SPU staff members. The first goal is to identify how much stormwater and groundwater needs to be removed from the piped sewer system for the areas that have sewer overflows during large storms. As part of this work we will be coming up with ideas for controlling, and conveying this water once it is removed from the sewer lines.  In addition, we will develop solutions to decrease the potential for significant stormwater flooding. We will bring these ideas to the Broadview Community during a public meeting. Background: The stormwater is most likely coming into the sewer pipes from direct connections of roof downspouts, and groundwater is likely flowing into the sewer pipes from sump pump connections and cracks in side sewers and mainlines, leading to sewer overflows in some areas during large storms.

Backflow Valve Installation Pilot Project (Reduces Potential for Sewer Backups into Homes) SPU contractors have installed 14 backflow valves so far. These valves are expected to greatly reduce the potential for sewer backups into residential homes that were identified as being at significant risk for future sewer backups, based SPU computer modeling results for the December 2010 storm. That storm was considered a 25-50-year 24-hour storm, and is our design level storm. We are still working with other residents in the area that are eligible for this pilot program.

Infiltration Reduction Pilot (in 12th Avenue NW area) SPU recently completed this pilot project to help reduce the chance of sewer overflows (SSOs) and backups into homes in the 12th Ave NW area.  SPU utilized 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 can allow stormwater and groundwater to get into the sewer system, especially during storms.  This pilot is considered a first step to reduce SSOs in the 12th Ave. NW area.

A total of 87 homes in pilot area participated in the program (95% participation rate). The flood grouting of the mainlines and residential side sewers occurred in August and September 2011. An additional fifty maintenance holes in the contributing area of the 12th Avenue NW sewer were sealed in January and February 2012.

SPU is monitoring sewer flows in this area to determine the reduction in flows after the flood grouting, and may utilize this method to seal additional sewers within the Broadview area. Earlier indications are that the flood grouting work was very successful in sealing the pipes.

Broadview Computer Modeling of Sewer and Drainage Systems and Flow Monitoring The Broadview computer modeling of the sewer and stormwater system has made significant progress and the sewer model for the Broadview area is expected to be complete in 3-4 weeks.  The stormwater system model is expected to be complete in June 2012.

Flow monitoring in the sewer and stormwater system continues to collect important data to inform the larger Broadview project. SPU needs the assistance of the Broadview Neighborhood related to the flow monitors in place.  If you see any of the following, please contact us at spu_broadviewprojects@seattle.gov:

•           Any vandalized flow monitoring enclosures

•           Anyone tampering with the flow monitoring enclosures

•           Debris built up in front of or behind the flow monitors and/or the weir structures

•           Loose equipment and/or wire bands floating in the drainage system.

Venema Creek Natural Drainage System (Green Stormwater Infrastructure) Project SPU is continuing to test soil conditions in the Broadview neighborhood to enhance our understanding of how well stormwater is absorbed on different blocks in the area. You may see contractors and large trucks with equipment in the area taking soil samples and conducting other tests. This in-depth analysis is needed to ensure that we find the best locations and use the best technology to solve problems with sewer backups and surface water flooding, while protecting Piper’s Creek from the impacts of stormwater runoff. We will share the results with the community as soon as they are available. 

Piper’s Creek Flow Control Study

SPU’s Piper’s Creek Flow Control Study continues. This two year study, which started in spring of 2011, is identifying the amount of stormwater coming into the Piper’s Creek from different areas in the creek watershed.  The project objective is to identify high priority stormwater management areas and actions in the Piper’s Creek watershed to reduce the impacts of stormwater runoff on Piper’s Creek.

Please let me know if you have any questions.

Sincerely,

Celia S. Kennedy, MPA

Capital Project Development & System Improvements SPU Drainage & Wastewater Division

(206) 684-4606