Why Option 1 is Best for Wilmette’s Storm Sewers

Wilmette has sewer issues, but we’re making progress. In terms of our basic infrastructure, the final piece of the puzzle is deciding what to do about the westside storm sewers.

The existing system is not capable of clearing runoff during anything more intense than a two-year storm.

The Village of Wilmette paid engineers to find solutions that will clear runoff and prevent property damage during 10-year storms (which have a 10 percent chance of occurring each year). This is a standard level of service for most communities.

The studies are complete. Next week, the Municipal Services Committee will solicit community input and decide which (if any) option to implement.

Options currently on the table include:

  • Option 1. Upgrade/replace sewer lines
  • Option 2. Underground storage tank at Community Playfield
    2.1 Above- and below-ground storage, with pump
    2.2 Only above-ground storage, drained by gravity
  • Option 3. Neighborhood storage (at three parks)
  • Options 1a, 2a, 3a, Same as 1,2,3 but with “ponding”

My personal opinion is that Option 1 is the best solution.

Storm Sewer Overhaul is a Necessity

First, while researching this blog, it’s become clear to me that doing nothing is like sticking our head in the sand… or under water!

We’re forced into action by a confluence of factors:

To understand the severity of the problem, here’s a mashup of westside rain stats and engineering estimates:

In the past 34 years…

  • Five 10-year storms occurred,
    damaging an estimated 120 structures/storm = 600 structures total
  • Four 100-year rain events occurred,
    damaging an estimated 700 structures/storm = 2,800 structures total

Many other storms also caused damage…

To make green initiatives feasible, and restore the level of service enjoyed in the 1950s, we must overhaul the storm sewers.

Why is Option 1 the Best?

I’d like to focus on the big picture.

The “ponding” options (1a, 2a, 3a) call for installing smaller diameter pipes than the full-priced solutions. However, the savings average only 10 percent, while property damage would increase drastically. Why install something that doesn’t work?

In my opinion, Option 3 is also out, because it does not achieve the required level of service (protection from 10-year storms).

That leaves Options 1 and 2.

I believe that Option 1, shown in the next map, is best.

Engineering Map for Option 1 (touch for full-size PDF)
Source: Village of Wilmette, Separate Storm Sewer System Stormwater Management Report, by Christopher B. Burke Engineering (January 2015), Exhibit 10.

Option 1 Attacks the Bottleneck Identified by Engineers

Engineers analyzed the westside using flow monitoring and hydraulic and hydrologic modeling.

The bottleneck is not the pumping system, and not the destination (the North Branch of the Chicago River can handle runoff from a 100-year storm).

Instead, the bottleneck is simply the sewer line capacity; Option 1 focuses on this.

Option 1 Upgrades More Pipe

With a focus on sewer line capacity, Option 1 specs call for removing 8,663 linear feet of old sewer lines, and installing 42,000 linear feet of new larger-diameter pipes. (To see planned replacement pipes, check the map for sewer lines marked R/R, like on Hibbard, Hunter, Romona, and side roads.)

By comparison, Option 2 specs call for removal of only 2,917 linear feet of pipe.

Replacement Will Mitigate Maintenance Costs

It’s true that replacing sewer lines for Option 1 is more expensive than relining pipes. But we shouldn’t forget that new pipes will require less maintenance, which should realize a small savings over the next decades.

In contrast, the storage tank options replace less pipe, while adding to maintenance costs for stormwater diversion, storage, and tank/pond drainage systems.

Option 1 Is More Predictable

Using the Community Playfields for below/above-ground storage has more unknowns.

For example, the USDA soil survey indicates that the water table is 6-24 inches below surface, but no core soil samples were analyzed to confirm this. I asked about the water table, and engineers say the project can be adapted to handle it.

Still, I’m concerned about cost increases as planners figure out:

  • Exactly how will local drainage be handled?
  • How will the project affect surrounding homes?
  • How will schools deal with a max. 8-foot-deep storm pond?
  • Will the tank/pond be discharged fast enough between storms?
  • If we select this project just to save money, will it?

In contrast, for Option 1, we know that:

  • Installing sewer lines is a standard part of road construction.
  • Back-to-back storms can discharge without delay into the Chicago River.
  • As an added bonus–replacing more storm sewer pipes will prevent stormwater from infiltrating any adjacent sanitary pipes.

Let’s Focus on Smart Implementation

Instead of searching for a way out, let’s start focusing on smart implementation.

Phased Construction

On the eastside, the relief sewer system has been constructed in phases, over a couple of decades, with completion expected by 2018.

Installing the relief sewers as part of regular road reconstruction has saved money. Why not use the same strategy for the westside storm sewers?

Focus on Funding

Currently, the only funding being considered is sewer fees, based on water usage, and issued as part of the water bill.

However, storm sewers are for clearing rainwater, not domestic sewage. Why not add supplemental stormwater utility fees, based on development of additional impermeable surface area, to help pay for upgrades that are required to handle increased runoff?

Finally, the village should hunt for any additional county, state, or federal funding that might be available. For example, village staff report that the MWRD might contribute $6-8 million–anything would help.


Links:

Learn more about probability and the chance of a “100-year storm” on the USDA site.

Learn more about phased construction and funding options, as described in the January 2015 Separate Storm Sewer Study.

Go to the Village of Wilmette webpage on the storm sewer meeting to get more information about the event, along with copies of the studies, and the meeting information packet.

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