Broadview Sewer & Drainage Improvements
Here are the notes from SPU big meeting on April 6th 2011.
COMMUNITY MEETING #1
Seattle Public Utilities (SPU) has been planning for a capital project to address sewer capacity and associated flooding in the Broadview area. The December 12, 2010 storm served to raise the priority of the project, accelerating the schedule, increasing staffing levels, and allocating funding.
The capacity of the sewer system in some areas of Broadview may be exceeded as rainfall reaches 2-3 inches in 24 hours. There is no single major source of stormwater inflow, but rather it is coming from direct connections to the sewer system (such as downspouts), from infiltration into sewer pipes, from footing drains, foundation drains and sumps. A multi-pronged approach is needed to keep stormwater out of the sewage system. This will include solutions which reduce side sewer infiltration, reduce inflow from downspouts, utilize backflow preventers, continue proactive maintenance, and conduct additional monitoring to inform design of long-term capital projects.
In 2011, SPU will conduct an Infiltration Reduction Pilot focused on the upper 12th Ave NW sub-basin, inspecting side sewers and grouting pipes. The first meeting for pilot candidates will be April 27. Affected property owners will be receiving an announcement flyer soon.
Also in 2011, SPU is proposing a Backflow Prevention Pilot as an interim measure for those with sewer backups. SPU will work with candidates in June to determine the feasibility and details of such a pilot.
For the long-term, SPU is planning a capital project to seal or replace existing sanitary sewers, to construct stormwater conveyance systems (including storage and treatment), to remove stormwater connections to the sewer system, and to upsize the sewer system in certain locations if needed. SPU will be working closely with the community to assess options, and will also be informed by the results of pilot projects.
On Wednesday, April 6th, 2011 from 6:00-8:00 p.m., SPU hosted the first of several community meetings to inform the planning phase of the long-term project, as well as to inform the public of planned and proposed pilots. Approximately 100 people attended. The purpose of the meeting was to provide participants with the opportunity to:
- Learn about the drainage and wastewater issues in Broadview
- Learn about SPU’s proposed approaches to the issues
- Provide feedback and ask questions
- Learn about next steps
- Give input on specific issue areas.
SPU will use the community input to inform the planning for both long-term and short-term alternatives that reflect community preferences.
Public Notification: SPU advertised the workshop through a postcard announcement mailed to approximately 3500 households in the Broadview area.
Format: At the beginning of the meeting, participants signed in as they arrived and SPU staff informed them of the meeting purpose and agenda. After signing in, SPU staff encouraged participants to review display boards and to give staff locations of issues. Participants had half an hour before the formal meeting in which to interact with SPU staff in this informal open house format.
Penny Mabie, Facilitator, welcomed the community to the formal meeting portion of the evening.
April Sotura, of the Broadview Sewer Task Force, talked about the 2007 storm in Broadview resulting in her and others forming the task force.
Nancy Ahern, Deputy Director of SPU, thanked the task force and the Broadview community for their ongoing support of the work SPU is doing. She explained that a plan for Broadview has been in the works for some time, but the 12/12/10 storm kicked it into high gear. SPU is committed to addressing the problems, and has raised the priority for Broadview capital improvements and storm response, with an accelerated schedule, increased staffing levels and funding allocated.
Gary Schimek, Separated Systems Manager, described the 4 drainage sub-basins in Broadview. Solutions may be different for each sub-basin. Smoke testing helped to identify direct connections. Flow monitoring measured infiltration and inflow. SWAMP (Surface Water Asset Mapping Project) and a sewer model have provided tools to assess impacts. He talked about sources of stormwater entering the sewer system, the distributed nature of the problem, and that capacity in the wastewater system is exceeded when rain reaches 2-3 inches in 24 hours. He discussed a proposed backflow prevention pilot; SPU will have a workshop with pilot candidate homeowners in June.
Martha Burke, Wastewater Strategic Advisor, explained that most side sewers in Broadview are 50+ years old. She discussed SPU’s upcoming Infiltration Reduction Pilot (see slides). The area chosen for the pilot (upper 12th Ave NW) was selected because we can monitor and measure improvement most readily there. If the pilot is effective, SPU will expand the program.
Jim Johnson, Project Manager for the long-term capital project plan, described the plan to seal or replace existing sanitary sewers, to construct stormwater conveyance systems (including storage and treatment), to remove stormwater connections to the sewer system, and if needed to upsize the sewer system in certain locations.
Penny reviewed next steps: SPU will email updates to the community, will meet with pilot candidates, will develop a project website, and will work with the Broadview Sewer Task Force to schedule the next community meeting, likely in September. Martha Burke was given as a contact for questions, (206) 684-7686. Penny then opened the floor to comments and questions.
Where questions were asked, answers follow in the secondary bullets. Please note that these comments are a summary and not an exact transcription of the meeting.
What is the difference between this backflow pilot proposal and the previous backflow proposal?
- The details of this program are still to be determined, will be decided in workshops with the community
What is the location of these backflow devices (in home, right of way, etc)?
- On private property between home and right of way
What if you are on a combined side sewer?
- On a case by case basis, we will have to figure out whether to reconfigure, put backflow upstream, etc.
Why choose upper 12th for the infiltration pilot?
- We can isolate and evaluate the success of the pilot there most easily.
Will it benefit people further down 12th? Will it benefit Carkeek Park?
- That is what we are expecting but the pilot results will show us how effective it is
- It is just one project; if it works we plan to expand it.
Problem seems to be only 10 years old, so how could direct connections be the cause?
- A study conducted in 1979 shows problems at that time
Is stormwater being addressed as well as sewage? When would GSI (green stormwater infrastructure) be implemented since it might help?
- We are looking at GSI for inflow reduction, probably not before 2013 since it takes time to develop.
Comment expressing concern regarding where downhill (believe this was a groundwater related comment) flow is coming from and whether natural drainage systems are contributing to the flow
When would natural drainage systems be implemented?
- Stormwater permit requires protection for creeks/Sound. Design takes time but needs to be in place before large scale disconnections of inflow because water needs to be put somewhere.
Why aren’t homes in Densmore basin included?
- They connect to a different part of system then Broadview, and will be addressed but not in the Broadview plans. [Ed. Note: First phase of Densmore plan will start in late 2011 into 2012.]
Is it that the sewer interceptor isn’t large enough? Where does the flow go if not backed up into homes?
- We need to remove stormwater from the sewer system.
- Upsizing the pipe would direct more flows to King County pump station which would then overflow more often.
Don’t side sewers produce the same problem with flow?
- Yes, that is why we are trying to reduce infiltration.
Where can you find information on the historic flows in the area? We get water bubbling up when there is no rain, and wonder if there used to be a creek.
- SPU has historic maps of creeks in the area, and UW Archives has records as well; these will be consulted in development of the long-term plan
Lots of groundwater, how do you manage that?
- SPU manages surface water not groundwater, but we consider the groundwater impacts related to inflow and infiltration, will need to consider in long term plan.
- Groundwater is generally managed by homeowners much like a creek; people often use sump pumps to mitigate the impacts.
Where should we put the stormwater?
- In our long-term project, we will be working on getting it out of the sewer system, creating an improved system to manage it.
Comment about impacts to Pipers Creek and treatment plant, specifically from new development on Greenwood Ave N – have you checked that they are in compliance on their stormwater management recently?
- Code only requires peak flow detention and discharge at rate that will not damage creek, so same amount flows but at a slower rate.
- Greenwood developments appear to be in compliance.
Can you give us incentives for disconnects?
- Yes, we will be evaluating as part of the overall approach.
Is anything happening regarding the Department of Planning and Development (DPD) not allowing new developments or reducing the amount of impervious surface in the area?
- City development guidelines are more stringent than required by the State Department of Ecology, with rigorous drainage review for anything flowing into Pipers basin.
What kind of a sewer system do we have?
- Separated system (sewage and drainage conveyed separately) with formal sewer pipes and informal drainage via ditches and culverts in most places
- Due to inflow and infiltration it is acting like a combined system (stormwater mixing with sewage).
Is anyone addressing the runoff coming down the hill?
- In some cases such as our Venema project, we will reroute stormwater. In other cases green stormwater infrastructure (like that currently at 107th & 110th) will slow flow to avoid erosion and reduce flooding potential.
Comment on problem with new construction channeling illegally, tree needing to be removed, too small of culvert
Comment expressing concern that 60 foot long ditch is full of water, nervous about more ditches being constructed (even natural drainage systems), don’t believe natural drainage systems worked in 1970 so they won’t now
- We dig test pits to see if soil is appropriate.
- Geological maps show hard pan in Venema, where we are planning natural drainage systems; successful SEA Streets and Broadview Green Grid are also located in this area.
In proposed backflow pilot, who will be responsible if the backflow preventers fail?
- We will be working with the community to figure out the responsibilities of each party and all the details of how this program would work.
- Will sealing sewer pipes create more stormwater flooding?
- Sewer backups in basements are our highest priority, but an important step in our planning process is devoted to mitigating this risk. We will also be reviewing groundwater data to ensure that reducing infiltration does not create more groundwater issues.
What about upgrading streets to channel and slow water?
- Yes, this could take several different forms i.e. Holman & 105th where we thickened the edge of the street during repaving. For 125th or 127th, we could look at shifting and completely rebuilding street.
- We have created berms and pipes to channel overflow.
Comment from Susan George that the questions tonight are all things that the task force has asked. Would like to see smaller workshops to address individual issues. We need guidance from SPU to help us help you.
Celeste Duncan Community Relations Development
Seattle Public Utilities
700 5th Avenue, Suite 4900
Seattle, WA 98124