Storm Sewer Project (FAQs)

The proposed storm sewer project for Wilmette’s westside has generated a lot of debate and confusion. It’s important to sift through the all the information to make a good 100-year infrastructure decision.

The latest Wilmette Village Board meeting on the storm sewers narrowed the potential solutions down to three options, including Option 1: Relief Sewers. For a comparison of each, along with maps showing which neighborhoods would (or would not) be protected, see our post on the Final Storm Sewer Options.

This post is my attempt to clarify the issues, with more background information, and the reasons why I believe Option 1 is the best solution. I’ve cited engineering studies and sources when possible.


How big of an issue is westside Wilmette flooding?
Currently, westside storm sewers frequently surcharge (i.e., back up), causing flooding even during mild (“2-year”) rainstorms, which have a 50 percent chance of occurring each year. Residents report (and a Cook County case study confirms) that the flooding makes people sick (due to bacteria-filled water and mold) and results in lost work time. Each flood event costs the impacted property owners $7K to $16K for cleanup and restoration.
Why is flooding such a big problem now?
We’re suffering a “perfect storm” of issues: Our storm sewers were installed in the 1920s-50s, back when the westside still had farms. Development has resulted in more buildings and pavement, which blocks infiltration of stormwater and increases runoff. Also, total rainfall levels and storm intensity are on the rise. In other words, Wilmette has grown, and the climate has changed, but sewer investment has not kept up with the demands.
What exactly is causing the flooding?
The bottleneck is the westside storm sewer pipes. They are woefully inadequate. There are not enough pipes, of large enough diameter, to convey stormwater at a fast enough rate, to the North Branch of Chicago River. Even a “2-year” storm clogs the system and results in flooding.

(Dump an entire 10-gallon bucket of water down your kitchen sink, in one big whoosh, and you’ll get the picture of what happens when rainstorms hit the undersized storm sewers.)

How will the Option 1 Relief Sewer Project fix this?
The project will add another storm trunk (i.e., big concrete pipe) to carry runoff west to the Chicago River. A network of new storm sewer pipes will flow into the trunk to drain the westside.

The existing pumping station (located at the river to “boost” flow) already has capacity for this upgrade, but minor improvements will ensure service is not lost during storms. (Currently, the pumps are operating at only 50 percent capacity, even during our worst storms. Option 1 will double the peak rate.)

Won't the Option 1 Relief Sewer cause downstream flooding?
No. Again, Option 1 simply creates the conveyance required during peak storm intensity to carry runoff over to the pump station. The overall total outflow is not going to differ that much per storm. Engineers analyzed Option 1 and found less than an inch of increase in river elevation downstream from Wilmette, even during a 100-year storm.


How bad is our flooding problem, in terms of financial losses?
To recover from 18 recent storms, westside Wilmette residents paid an estimated $45M to $87M for cleanup and recovery. In addition, damp basements and unresolved flooding issues will likely reduce the overall value of westside property by $21M to $110M.
How much will the Storm Sewer Project cost?
In today’s dollars, the estimated cost is $80M to $95M, depending on some identifiable variables, which Stantec, an engineering consulting company, is currently researching and will present at the September 25 Storm Sewer meeting. (Both the low and high cost estimates include a 20 percent contingency fee, to handle unforeseen complications.)
Is it true the upgrade costs $227K per protected property?
In short, no. That misconception comes from a 2015 study, which relied on a single quick calculation to compare stormwater solutions. Engineers showed that the Option 1 Storm Sewer Project protects more homes from infrequent but severe “100-year” storm damage, at a lower cost per home, than other options (of 700 homes expected to be damaged, 330 would be completely cleared of flood water, at a cost of $227K/home).

However, that number doesn’t tell the whole story. It only examines the 700 homes guaranteed to flood up to, or into, doorsills, during “100-year” storms. In reality, many more homes experience damage much more frequently, during “10-year” storms, when flood water rises midway up the property, saturating the ground.

For these frequently flooding properties, Option 1 provides a solution, by draining the entire westside for up to “10-year” storms. In other words, frequently flooding properties would experience significant relief with the Option 1 Relief Sewers. (This chart from the 2017 Value Study provides a comprehensive cost/benefit analysis for westside protected properties.)

In addition, investing in storm sewers can reduce the severity and duration of flooding during all storms, prevent sickness from mold and bacteria, reduce the loss of work hours to deal with flooding, reduce stormwater infiltration and backups in the sanitary system, and cut down on degradation of roadways, sidewalks, and other infrastructure maintained by the village. Thus it’s not true that the cost per unit of benefit is $227K.


Why can't we just open the locks when the westside sewers back up?
Because westside sewers have no connection to the locks. The locks on the Northshore Channel at Wilmette Harbor provide relief for the eastside combined sewers (serving Lake Michigan to Ridge Road). The drainage area west of Ridge Road has a sanitary sewer (for toilet sewage) and storm sewer (for runoff).
Can’t individual property owners do their own floodproofing?
The short answer is no. It (literally!) takes a village (and MWRD) to provide adequate infrastructure, without which, floodproofing systems won’t work. Many westsiders have spent $20,000 (or more) to install drain tiles, sump pumps, flood control or overhead sewer systems, etc. Despite all of this personal expense, it does not stop the street and basement flooding problem because the storm sewers are still inadequate.
When it floods, the discharge spots for sump pumps and detention tanks get submerged (in other words, the place where the water is supposed to come out is itself underwater), rendering these expensive floodproofing systems useless. Stormwater pours over door sills and through low-level windows. Season after season of high groundwater attacks cement foundations.
Can't the village buy property, and knock down the homes that flood?
That’s an extremely unlikely option. Although the MWRD supports acquisition of properties that are located on flood plains and repeatedly damaged, with no possible remedies, those criteria don’t apply to Wilmette. Most westside Wilmette homes are not located within a flood plain identified by FEMA/NFIP, and remedies are available.

Even if buyouts were an option, it would be more expensive to acquire properties than to simply fix the sewers. For example, Option 1 gives 120 homes complete protection from 10-year floods at a cost of $80M-$95M, or less, and also provides some protection for more than 700 homes. The average Wilmette home value is $629K. So buying 120 homes would cost $75M, or 700 homes would cost $440M. Also, tearing down homes eliminates tax revenue from the properties. It seems clear that property acquisition would be more expensive than investing in the sewers.

Why didn't the village search for less expensive green solutions?
They did, but green solutions won’t solve the problem (or even significantly reduce flooding). Green infrastructure, such as rain gardens, could be integrated with Option 1 where feasible to reduce pollutants in the waterways, and to mitigate runoff for less intense storms. But conditions on the westside are challenging, making green infrastructure a supplement, not a substitute, for adequate drainage.

Consulting engineers analyzed and reported on green solutions as part of overall stormwater analysis, finding that the expected “green” impact is low or implementation not feasible in some areas of the westside.

For example, detaining runoff from an average westside home, for a moderate storm, would likely require 60 rain barrels, which is not a solution. Engineers also looked at local storage areas, to serve as detention ponds, but Wilmette has very little undeveloped green space. In addition, the ponds require grey infrastructure to direct runoff into them, and drainage time is required to recharge after each storm.

Engineers recommended setting up rain gardens, but many areas of the westside have low-infiltration clay soils, and the impact would be highest for mild rainfall, not intense storms. A recent Stantec engineering report on green infrastructure options found that permeable pavers could be a worthwhile possibility in some areas, but impact on flood levels would be limited.

Decision Timeline

Why are we rushing into this?
We aren’t rushing. The village has been looking into this for almost a decade.

For example, in a 2009 email, past Wilmette President Chris Canning acknowledged ongoing complaints from residents about westside flooding and property damage (caused by storms in 2007, 2008, and 2009). He explained that the westside storm sewer system is “self restricting because of the finite capacity,” and promised the village would look into it. Since then, Wilmette taxpayers have funded more than three major engineering studies. The board reviewed the issues and proposals for too many hours to count.

Shouldn't we get a second opinion, or verify the Option 1 plan?
Yes, and yes. We should do all of that — and we have.

During the past decade, Wilmette taxpayers have spent more than $859K (in today’s dollars) for extensive engineering studies on westside stormwater management and sewers.

Check it out:

2009-2010 Separate Sewer Study: Provided a big picture of westside flooding and sanitary/storm sewer issues, including lack of westside storm sewer capacity. The proposed solutions included adding a new westside storm trunk and additional storm sewer pipes.

2013 Sewer Flow Monitoring Study: Focused on the sanitary sewer, but also mentioned “storm sewer‐to‐sanitary sewer cross connections.” Provided preliminary research for the West Park storage tank.

January 2015 Separate Storm Sewer Study: Engineers created hydraulic/hydrologic models to analyze westside flooding and sewer problems, using geographic information system (GIS) mapping, land elevation data, sewer maps, and rainfall data. The models were calibrated using sewer flow metering, and residents’ reports on flooding. Based on the models, engineers proposed three solutions, including the Option 1 Relief Sewer Project.

April 2015 Follow Up Study: Looked for cheaper alternatives to Options 1, 2, 3, like using smaller sewer pipes or substituting detention ponds, but found that Options 1b, 2b, and 3c were not more cost-effective or feasible than Option 1, which attacked the root cause (inadequate storm sewer pipes).

2017 Value Study: Confirmed that the Option 1 Relief Sewer project is a sound solution. The final presentation at Wilmette Village Hall on September 25 will include research on construction efficiencies.

Can't we slow down to search for a less expensive option?
Ten years of extensive studies and debate have proven that, unfortunately, there aren’t any alternatives that are cheaper than, and also as effective as, Option 1.

As part of the current “value” study, Stantec engineers may identify some cost savings (e.g., digging instead of tunneling in some sections, or using prefab junctions instead of making junctions on-site).

Wilmette President Bob Bielinski asked Darren Olson of Christopher B Burke Engineering if Option 1 is a prerequisite for other improvements (like rain gardens or home flood control), and the answer was: “Absolutely!”

You almost never hear an engineer say anything is “absolutely” necessary, but in this case, better drainage is a basic requirement for effective stormwater management.

Meanwhile, as the slow decision-making process drags on, westsiders have continued to pay for flood damage with every big rainstorm.

Isn't Wilmette required to have a referendum on any upgrade?
No. The Wilmette Village Board members are required by law to vote on any sewer improvement, with a majority determining the outcome. A public referendum could only serve as an advisory action. In other words, even if a village-wide referendum were held, the board members themselves would still be required to vote on which upgrade, if any, to authorize.

Nonetheless, the Village of Wilmette has conducted a three-month educational and outreach campaign, including numerous online and in-person opportunities for residents to ask questions about stormwater management and voice opinions about upgrade options, thus providing more access for public input than a single referendum would offer.

Finding the Funds

Doesn't Wilmette have Special Service Areas to pay for sewers?
No. Wilmette has discussed setting up SSAs as an option for some cosmetic types of upgrades that particular neighborhoods might choose to fund. But sewers are a basic public service, paid for by all residents.
Is it fair to make everybody pay for westside sewers?
Again, sewers are a basic public service, paid for by all village residents. For example, all property owners in Wilmette have paid additional sewer fees to fund the eastside relief sewer, which will have a final total cost of approximately $43M to $61M in today’s dollars. (The eastside relief sewer was constructed in phases, starting with the main trunk, then sections were added during road construction when possible. So costs are tricky to pin down, and planning for expansion continues.)

Likewise, the entire village is paying, via sewer fees, for the West Park Storage tank, which helps prevent sanitary sewer backups, west of Romona Road.

Also, we all pay MWRD taxes, which helped fund three eastside projects: TARP overflow relief, the Wilmette lock upgrade, and the Green Alleys project.

Eastside sewer infrastructure has been upgraded to provide a minimum of 10-year storm protection, the same standards should apply to the westside.

Are there other ways to fund this?
So far, the Wilmette Village Board has focused on increasing sewer fees to pay for the storm sewer project.

For example, Stantec engineers estimate that the average annual sewer fee would increase $46 for every $10M in debt issued. Wilmette Finance Director Melinda Molloy said the village could ramp up borrowing, as the project is phased in. At the high-end, by 2047, the average annual sewer fees would have a peak average increase of $514, then the 30-year General Obligation Debt would be paid off.

Here are some other options that municipalities use to fund sewer projects:

Storm Utility Fees: Developers and property owners pay fees based on the percentage of impermeable land on a property. This has the advantage of discouraging development that adds to stormwater management problems, while encouraging creative solutions. Communities like Downers Grove are using these fees.

The MWRD: The county sewage district might help fund a new storm trunk, which is the main pipe to the river, as an MWRD Stormwater Management Phase 2 project. (See examples of past investments on page 7 of this MWRD document.) Historically, the MWRD has funded about 50 percent of proposals, possibly at $100K to $1M level. To get a chance to receive funds, an application would be due by February 16, 2018. The Wilmette Village Board would need to speed up their decision-making process to meet the deadline.

IDOT/MFT: Illinois Department of Transportation (IDOT) manages the Motor Fuel Tax (MFT), which we all pay at the gas pump. The funds help pay for roadway improvements, like storm sewer drainage pipes, to bring roads up to standard. For westside Wilmette, the standard should be 10-year storm protection (as explained in the BLR manual, section 38-2.02). Illinois Transportation Enhancement Program (ITEP) could provide up to $2M funding per project.

ILEPA: There is an extremely slim possibility that Wilmette could get EPA funding, but we would have to prove the project helps keep local waterways cleaner — a tough sell. Currently, stormwater infiltrates the sanitary sewers, overwhelming the treatment plants and causing sanitary backups. But we don’t have exact data on the reduction in stormwater infiltration that Option 1 would provide.

Why is Option 1 Relief Sewers our best investment?

Studies confirmed it's the best for our goal.
The Village of Wilmette spent eight years (and $859K in today’s dollars) on engineering studies, conducted by multiple engineering firms, to triple-check options and cost estimates. Engineers verified Option 1 is the best solution to achieve the board’s original goal: 10-year storm protection throughout the westside. (See the maps of the options for comparison.)
Capacity of existing infrastructure will be fully utilized.
It’s the only option that fixes the main bottleneck (storm sewer pipe capacity). By adding more pipes of larger diameter, the system will (finally!) use the full pump station capacity and full outflow permitted to the river.
It's a foundation for any future stormwater projects.
Option 1 is a prerequisite and foundation for any additional stormwater projects.

In contrast, Option 4 Neighborhood Storage can’t be expanded, due to a lack of additional vacant storage space. Also, Option 4 does not include a new storm trunk (pipe) to carry runoff to the river, so it wouldn’t support an expanded network of storm sewer pipes.

Likewise, Option 2 Relief Sewers + Neighborhood Storage lacks a full-sized trunk to convey stormwater to the pump station and river, so it would be difficult and costly to upgrade the entire westside to a 10-year standard, sometime in the future.

Recharging capacity will be helpful for all storms.
Once detention ponds fill, they offer no relief, until they’re drained, which is a problem for back-to-back storms. In contrast, Option 1 Relief Sewers will continuously drain, or quickly unclog once rain abates during 100-year storms. Another concern for above-ground storage is that neighborhood detention requires a deep pit for stormwater, posing safety concerns.
The value is best, considered as a 100-year investment.
Option 1 is the best value per taxpayer dollar. The cost per property protected from 10-year storms is competitive with other options. Coordinating with roadwork or water main replacement can save money. This option also replaces some old undersized storm sewer pipe, which eliminates the maintenance costs associated with those old sections of the system.
It's equitable for all of Wilmette.
It’s the only upgrade that leaves no neighborhoods behind. The project can provide 10-year storm capacity to the entire westside (assuming a few properties are helped by the current Hibbard/Skokie upgrade). The project brings the entire westside up to the same standard as we already funded for the eastside.

Voice your opinion to Wilmette village trustees at

And comments are welcome (below). Contact me or post on Facebook if you have additional questions.


  1. Herb July 28, 2019
    • karleensm July 28, 2019
  2. Tom Palmer March 15, 2018
    • karleensm March 16, 2018
  3. Julie Wolf September 23, 2017
    • karleensm September 23, 2017

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