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IDOT Blog – Thursday, May 19, 2022
Look Out Below! I-290 Pump Station Takes Shape
That large hole you see forming along Interstate 290 is going to keep you dry for a long time.
Since 2019, IDOT personnel in District 1 covering Cook and the collar counties have been replacing what’s known as Pump Station 4 along the interstate.
Planning for the replacement began about 20 years ago as part of the preliminary engineering study for the eventual reconstruction of I-290 (Eisenhower Expressway) between U.S. 45 and Central Avenue. Ensuring a modernized facility that meets current design standards is one of the first components required for the reconstruction of the expressway. When completed, this will be the second-largest pump station in District 1, located next to the Des Plaines River, at 70 feet deep.
During planning, dynamic modeling was used to assess the pump-station hydraulics to account for items like potential overflow issues. This more reliable type of modeling made evaluating possible solutions easier. Due to the size of the station, planning also included physical modeling of the pump layout, so the final design would provide easy flow into the pumps and allow them to function properly.
Reconstruction of the expressway requires that the pump station be rebuilt to meet design criteria and modernize the aged facility. The new station will include 10 pumps, two of which are standby pumps that can be used in case a main pump fails or needs servicing. Each main pump is a 440 horsepower, three-phase 4,160-volt pump that can discharge 22,500 gallons per minute. In certain situations, one standby pump activates to provide the necessary level of protection. Two 7,000 gallons per minute low-flow pumps handle most drainage until a larger storm event calls for the main pump(s) to activate. Runoff that exceeds the maximum pumping rate will be stored at various locations throughout the system when the expressway is reconstructed.
The new station will include 10 pumps, two of which are standby pumps that can be used in case a main pump fails or needs servicing. Each main pump is a 440-horsepower, three-phase 4,160-volt pump that can discharge 22,500 gallons per minute. If there is an issue with a main pump, one of the standby pumps activates, ensuring the necessary level of protection. Two 7,000 gallons per minute low-flow pumps handle most of the standard drainage until a larger storm event occurs, calling for the main pump(s) to activate. Runoff that exceeds the maximum pumping rate will be stored at various locations throughout the system when the expressway is reconstructed.
The large station size requires a higher level of electrical service than the typical design and posed a construction challenge due to the required depth. This was solved by the formation of a secant wall that provides soil retention to allow excavation for the new pump station. The secant wall will cost more than $5 million and required over 100 micro-piles to support a stabile area that could be excavated for the new pump house and wet pit. The existing wet pit will be salvaged and connected to the new station. This will allow the existing trunk sewer to remain and provide a grit chamber that helps settle solids that are too small for the trash rack to catch before they reach the pumps.
The site encroaches into the floodplain of the Des Plaines River and additional storage was provided to help minimize capacity issues. The grading plan was designed to allow the pump discharge to flow through this area before reaching the river, providing for energy dissipation and improved water quality.
While there are no plans to start the larger reconstruction of I-290 any time soon, the department continues to explore possible design options and funding solutions.