Storm Sewer Project (Value Study)

The Wilmette Village Board Storm Sewer meeting on September 25 was devoted to the Value Study presentation by Stantec, an engineering consulting firm. Engineer Joe Johnson patiently reviewed every finding, chart, and graph and answered board members’ questions. (The Value Study is also part of the November 27 Storm Sewer Meeting Packet.)

Here’s the first important map from the presentation:

Current flooding during a “10-year” storm. To help find solutions, the engineers identified all the areas that need storm sewer relief (i.e., most of the westside!).

Bottom Line

To protect the entire westside from “10-year” storms, the most cost-effective plan is Option 1: Relief Sewers, with a new network of pipes (40,000 linear ft) draining into a large pipe to convey runoff to the existing westside pump station, which “boosts” the stormwater into the North Branch of the Chicago River.

This confirms the 2015 Burke engineering study; no big new findings.

Cost = $80-$95 million (includes 20% contingency.)

Proposed westside storm sewer project, including a new storm trunk (in yellow along Lake Ave, at left) and network of new pipes (also in yellow). Joe Johnson assured us that even the few blue flooded areas could be served by making a few tweaks during the engineering/design phase.

Alternatives

The board asked for alternatives to save money. Again, confirming the Burke study, the only way to save money is to reduce storm sewer performance or leave sections of westside Wilmette out of the upgrade.

Cost = based on coverage
(for example, ~70% westside protection for ~70% cost)

To determine whether your neighborhood is under consideration to be “left out,” check the maps:

Reduced relief sewer, along with some localized stormwater storage (light blue square). The dark blue areas show flooding during a “10-year” storm in areas left out of the upgrade.

Reduced relief sewer. The dark blue areas show flooding during a “10-year” storm in areas left out of the upgrade.

The Surprise Ending for the Meeting

Here’s the surprise announcement, made at the end of the three-hour meeting by the village staff (paraphrased here):

Since all the westside Wilmette infrastructure was installed in the 1920s to 1950s, many of the systems are end-of-life…including the water service. Many of the water mains on the westside must be replaced, and the village is already planning the upgrade. Replacing water mains at the same time as storm sewers could reduce overall infrastructure costs.

This is a mind-boggling revelation…

Is the village seriously considering NOT upgrading the storm sewers? In other words, when the village digs up much of the westside to replace the water mains, are they going to just look at the undersized sewers, then cover them up again?

How does this make sense, from a 100-year planning perspective?

Next Steps

Residents can immediately email trustees to advocate for a functioning westside storm sewer (find email addresses at: https://www.wilmette.com/village-board/).

Village President Bob Bielinski said there will be at least two more meetings on: finances, and decision-making.

Nitty Gritty Details

For those of you interested in the “deep dive,” here are some more details:

Downside

  1. Big constraints for westside are:
    • Low elevations limit the natural pathways for overland flow;
    • Edens highway blocks access to river and exit points for runoff,
    • Development has reduced open space for storage.
       
  2. Trustees asked if “10-yr” storm protection is typical protection. It’s the typical minimal standard of service.
     
  3. The entire world is working to reduce climate change so… Wait a minute. Nope. Climate change poses a continued risk.
     
  4. Design decisions could reduce costs only 5% to 10%, at most.
     
  5. Lake Ave would need to go to 2 lanes for weeks/a couple of months.
     

Positive Points

  1. The board was given time to ask any technical question, a “speak now or forever hold your peace” phase of commitment.
     
  2. After doing initial designing, planning,and core soil samples, there will be very low risk of cost overruns for Option 1. (Tunneling under Edens is doable…)
     
  3. The board appears to understand that they are choosing infrastructure for the next 100 years of the westside…
     
  4. Stantec clarified the extent of flood impact by using a slightly different formula to identify two types of problems:
    • Impacted structures:
      Water within 50-foot circle = 311 (for 10-year storm)
    • Flooded properties
      Water anywhere on lot = 1,268 (for 10-year storm)
       
  5. More pipes (conveyance) makes Option 1 a better choice than storage because pipes continue to have an outlet. Once storage fills, you have to wait for drainage before it works again.
     
  6. We already have a pump station and permit to handle the increased rate of flow for the Option 1 outlet onto the North Branch of Chicago R.
     
  7. Option 1 radically reduces the duration of 100-yr floods, cutting depth by ~10% and drainage time by ~70%. A big win!
     
  8. The project could be phased so each area is just ripped up for a single season (weeks/couple months each).
     

Why Some Other Options Won’t Work

  1. Ripping down flooded homes to create local storage would not work: it’s too expensive, and the flat topography makes it difficult to contain water.
     
  2. “10-year” storms now come every 5-7 years. But it would be costly to scale up Option 1 to provide true 10-year protection because it’s already in a sort of “sweet spot” given the constraints and financial concerns.
     
  3. Green infrastructure doesn’t reduce flooding much during severe storms and can be costly to maintain, but could help with improving general water quality for water flowing into the river during lighter rainfall.
     

Funding is TBD

  1. Storm utility fees could reduce reliance on water fees.
     
  2. MWRD funds could help–if we prep with more planning to apply for it on time.
     
  3. Also, overlap in water main replacement and storm sewer upgrades could save on overall infrastructure costs. (Still trying to get some numbers for this…)
     

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