Broadview Sewer Investigation

This report summarizes the results of a study of the sanitary sewers in the Broadview area conducted over 2 years from 2008 to 2010. Broadview is located in northwest Seattle and includes the area between NW 130th Street, NW 105th Street, Fremont Avenue N, and NW Blakely Court. The study investigated alternatives to improve the performance of Broadview sanitary sewer system.

Five problem areas were identified as the focus for analysis based on the data collected and four alternatives were developed and evaluated to improve capacity. In addition, other options of a preventive nature including enhanced maintenance and use of backflow preventers were examined.

  • Alternative 1: Problem areas at 1st Avenue NW and NW 115th Street, and at NW 105th Street were addressed by removing capacity constraints to reduce the risk of backups.
  • Alternatives 2 and 3: Potential effects were modeled for reducing respectively inflow or infiltration to the capacity of the system. A range of theoretical scenarios were modeled to test the sensitivity of the system to this approach.
  • Alternative 4: A combination of both inflow and infiltration was modeled to determine if this would provide improved capacity for 12th Ave. NW.

Besides these specific areas, the study also includes recommendations that are area-wide in nature, such as the value of reducing inflow through the use of Green Stormwater Infrastructure (GSI) where possible and cost-effective.

It should be noted that this was an investigative study, and does not represent a preliminary engineering report. Before specific projects are designed to be included in SPU’s capital improvement plans, a more detailed analysis of the cost and benefits of the options is done, compared to other possible projects, and funding identified.

The newly completed Broadview study is summarized in the Project Summary Report (pdf). (Figure 4 – detailed map of study area, pdf). Additional information about the study area is included in the Problem Identification Technical Memorandum (pdf), and the supporting modeling is described in the Modeling Report (pdf).