The Western Ingersoll Basin is a drainage area divided north and south by I-235 and bounded by 31st Street (east), 45th Street (west), Grand Avenue (south), and University Avenue/Forest Avenue (north).
The Western Ingersoll Sewer Separation project will upgrade the Western Ingersoll Basin to prevent combined sewer overflows, reduce flow to the Des Moines Metropolitan Wasteland Reclamation Facility, and comply with State requirements.
Goal: Separate the stormwater and sanitary sewer flows into separate systems (storm sewers and sanitary sewers) to reduce flow to the Des Moines Metropolitan Wastewater Reclamation Facility and prevent Combined Sewer Overflows (CSOs).
Combined sewer systems are sewers that are designed to collect rainwater runoff, domestic sewage, and industrial wastewater in the same pipe. Most of the time, combined sewer systems transport all of their wastewater to a sewage treatment plant, where it is treated and then discharged to a water body. During periods of heavy rainfall or snowmelt, however, the wastewater volume in a combined sewer system can exceed the capacity of the sewer system or treatment plant. For this reason, combined sewer systems are designed to overflow occasionally and discharge excess wastewater directly to nearby streams, rivers, or other water bodies. Dealing with combined sewers are common issue faced by many river cities (14 in Iowa, and 772 in the U.S.).
In 2003, City of Des Moines developed a Long Term Control Plan as part of the National Pollutant Discharge Elimination System (NPDES) Permit required for the operation of the Des Moines Metropolitan Wastewater Reclamation Facility which included a phased approach for capital improvements for the Long Term Control Plan, which will eliminate the number of CSOs in 2000 from 20 down to only one located at the Wastewater Treatment Facility by end of 2023.
In 2010, the City, Des Moines, the Des Moines Metropolitan Wastewater Reclamation Authority, and the State entered into a Consent Decree which established a time schedule for the completion of major elements of the Long Term Control Plan. This includes eliminating the Combined Sewer Overflow at 22nd Street and High Street by December 31, 2023.
The Western Ingersoll basin is located in the western part of the City of Des Moines generally bounded on the east by 31st Street, bounded on the south by Grand Avenue, bounded on the west by a line located between 44th Street and 45th Street and bounded on the north by an irregular line located between University Avenue and Forest Avenue.
The sewers in the Western Ingersoll basin are tributary to the Ingersoll Run Combined Sewer. The Ingersoll Run Combined Sewer is tributary to the Wastewater Reclamation Authority’s (WRA) Combined Sewer Overflow (CSO) at 22nd Street and High Street.
The total area of the Western Ingersoll basin is approximately 820 acres; however, the Western Ingersoll basin consists of two (2) separate basins, one (1) basin north of I-235 and one (1) basin south of I-235.
The southern part of the Western Ingersoll Run basin located south of I-235 is completely combined with no separate storm sewers. South of I-235, there are over 30 existing storm intakes connected to the combined sewer system.
Several storm sewer systems exist in the northern part of the Western Ingersoll basin (located north of I-235); therefore, the northern part of the Western Ingersoll basin is only partially combined. North of I-235, there are approximately 20 existing storm intakes connected to the combined sewer system.
The City has developed a plan for sewer separation with recommended improvements which include removal of the storm intakes off the combined sewers and construction of new separate storm sewer systems along with green infrastructure, including pervious pavement and underground aggregate storage to reduce stormwater volume and runoff rates. These improvements will be constructed in three phases starting in 2021 through 2023.
Phase One will separate sewer systems in the area south of I-235 through the installation of over 10,000 LF of dedicated storm sewer along:
Ingersoll Avenue from 31st Street to 42nd Street
Woodland Avenue from 38th Street to 42nd Street
Pleasant Street from 39th Street to 41st Street
38th Street from Ingersoll Avenue to Woodland Avenue
39th Street from Woodland Avenue to Pleasant Street
The new storm sewer system will outlet to a previously constructed 6-foot by 6-foot culvert terminating on 35th Street, just north of Ingersoll Avenue. Existing storm sewer intakes, currently flowing into the Combined Sewer system, will be disconnected and removed.
Project Status
2018 — Western Ingersoll Sewer Separation Study Completed
December 2019 — Design Agreement Finalized
January 2020 — Preliminary Design
February 2021 — Final Design
February 2021 — City Council to Order Construction
Spring 2021 — Project Letting and Construction Contract Awarded
