Gilmore Avenue Sewer Separation

The Gilmore Avenue Sewer Separation Project is part of Omaha’s Combined Sewer Overflow (CSO) program designed to improve the city’s water quality.

Our team was hired to help the city remove stream flows from the combined sewer system and provide neighborhood sewer separation to meet the CSO program’s goals. The project included a watershed of approximately 350 acres and features the design and construction of:

  • A regional detention basin
  • 3,000 linear feet of large diameter storm sewer interceptor
  • New storm and sanitary sewer collections systems covering 150 acres
  • Green infrastructure to improve water quality and attenuate flows

More than half of the watershed is located in Bellevue, Nebraska, south of Omaha. A small, intermittent drainage conveys flow from Bellevue to the Omaha CSO. When analyzing the watershed and downstream infrastructure, our team determined the downstream infrastructure was undersized to convey the design storm and separate the neighborhood sewers. To address this issue, the design team analyzed the watershed with a regional detention basin and a lower level level of service. The level of service for the separation area is better than existing conditions, allows for full separation of the neighborhood, and provides for additional capacity in the downstream infrastructure to allow future separation.


Omaha, Nebraska, Public Works Department


Omaha, Nebraska


Inflow & Infiltration Reduction

Sewer Separation


Government, Military & Municipal


The existing 60-inch brick sewer is being replaced by an 84-inch reinforced concrete pipe storm sewer and 18-inch clay sanitary sewer. The regional detention basin will store the 10-year event, and safely pass the 100-year event through the auxiliary spillway. The design level of service for the project is a five-year design storm.

The 84-inch storm sewer crossed two mainlines of the Union Pacific Railroad and beneath a Nebraska Department of Roads viaduct. The large diameter storm will be tunneled under the railroad and tie in to an existing stub-out from a previous project. Because the project watershed spanned two cities and counties, significant coordination was performed to keep an open dialog with both communities for design and public engagement issues.