Part 2: Wilmette Official Answers Readers' Flood Questions

Wilmette's flood survey has conjured in the blog section of our site. A Patch reader and blogger's conversation sparked some interest from Wilmette's Director of Engineering Services, Brigitte Mayerhofer.

Earlier:

Mayerhofer reached out to Patch to answer the concerns raised. Below is the second part of the Q&A. In the final round, Mayerhofer explains the feasibilty of certain flood alleviations:

4. I understand the Village was "lining" the sewers to prevent infiltration of ground water into the sewers, but doesn't lining in effect reduce the capacity of the sewers?
In the answer to number 2, it is noted that pipe roughness impacts the flow. One of the benefits of sewer lining is that the newly lined pipe has a smooth and continuous surface. Compared to the old clay pipe with a high friction factor, the newly lined pipe actually has a higher flow capacity. The sewer liner is only a few tenths of an inch thick, so the reduction in roughness coefficient more than makes up for the minimal change in pipe diameter.

5. How feasible are any of the following solutions:

• Check and Disconnect ANY storm water discharge from entering the Sanitary sewers (in effect convert the combined sewer into a dedicated Sanitary Sewer).
  In the combined sewer area east of Ridge Road, all of the storm or “clean” water sources could be disconnected from the combined sewer but then a separate storm sewer system would have to be built. The cost for accomplishing complete sewer separation is well over $100 million and therefore cost prohibitive. The afore-mentioned relief sewer project essentially serves as a partial separation, but only in those areas of the system that are prone to surcharging. Most recently, all of drainage structures on Sheridan Road were disconnected from the combined sewer and are now conveyed in a separate storm sewer that discharges to the North Shore Channel. While ideal, this approach is not cost effective throughout the entire east side.
  
  On the separate sewer side located west of Ridge Road, the Village routinely looks for illegal storm water connections to the sanitary sewer. When identified, these circumstances are treated as code violations and corrected. The exception to this is gravity-fed foundation drains that in the 1980’s were deemed too cost prohibitive for the home owner to disconnect.

• Increase the size of sanitary sewer.
  The Village has over 154 miles of sewers. Sewer lining is a more cost effective method of increasing capacity through infiltration reduction compared to rebuilding the entire system which is cost prohibitive.
  
  
• Install "backwater valves" or "flapper valves" on branches to homes affected.
  
  While any method of protecting your home from sewer backups is a good investment, the best option is an overhead sewer. An overhead sewer system includes a sump installed under the basement floor to intercept sewage flowing from basement fixtures, including the basement floor drain. An ejector pump in the sump lifts sewage up above flood level so your home is protected by an elevation difference.
  
  From there the flow drains by gravity into the sewer lateral.
  A sewer backup valve is a less costly option but not as reliable as an overhead sewer system. This system requires routine maintenance to ensure the valve operates properly. Sewer valves are typically installed in an underground structure in the yard, so the construction impact is less disruptive.
  
  
• Offer financial and other guidance and help to have affected home owners install sewage ejectors (essentially sump pumps) for basement plumbing fixtures.
  
  The Village of Wilmette does not currently offer a cost-share program for the installation of overhead sewers. An overhead sewer program and a similar program to encourage maintenance of sewer laterals are included in the Village’s capital improvement program for future discussion and possible implementation.
  
  In addition, the Village’s website, www.wilmette.com, contains information on two resident assistance programs, including flood assessments and sewer lateral maintenance. The Village received proposals from several companies to establish set rates for these services based on a defined scope of services.
  
  For home owners who are not quite sure how or why they experience flooding, it may be beneficial to hire a consultant to perform an independent flood assessment of your home.
  
  Unlike companies who have a product or a service to sell, an independent engineer will be able to diagnose the cause of flooding and provide suggestions to mitigate the flooding.
  
  Similarly, residents who have not performed any maintenance on their sewer lateral should consider hiring a plumbing company to clean and televise the pipe. The condition of your sewer lateral will determine if groundwater is infiltrating the lateral and contributing to sewer backups. It will also ensure that there are not any tree roots or accumulated debris blocking or slowing the flow from the home. Sewer laterals can also be lined to eliminate groundwater infiltration and preserve the structural integrity of the pipe.
  
  The link for the resident assistance programs and other storm water management tips is http://www.wilmette.com/departments/stormwatermanagement/default.aspx.

For more questions regarding this information, contact Brigitte Mayerhofer, P.E., Director of Engineering Services at 847.853.7627. Join the discussion on storm recovery on Wilmette-Kenilworth Patch's Facebook page.