Sewer Separation Project Improves Water Quality

Concrete pipe was used to install storm and sanitary sewers on the $15.8-million Nicholas Street Phase 1 Project in Omaha, Neb. The project helped improve water quality in the Missouri River by removing a large volume of storm water runoff from a combined sewer system, and increased storm sewer capacity in an underserved area.

Three 108-in.-diameter storm sewers and one 24-in.-diameter sanitary sewer were extended; an existing combined sewer was removed and replaced with a new storm and sanitary sewer; and a new sanitary sewer was constructed. The project involved one railroad crossing where jack and bore methods were required. All pipes were constructed with confined O-ring joints. 

The combined sewer was rebuilt as a new 42- to 72-in.-diameter storm sewer system. The 24-in. sanitary sewer is designed to provide a separate sewer. Upon full extension, it will allow the city to eliminate a sanitary pump station.

All four pipelines were constructed in one trench. Type A riprap and geogrid were used to stabilize the bottom of the trench and 3-in. crushed limestone was used as pipe bedding material to the spring line of the pipe. The pipe bends were constructed using precast 108-in.-diameter bend sections. 

The
108-in. reinforced concrete pipe (RCP) was produced in 8-ft lengths using a dry-cast method to ASTM Specification C-655 with a D-Load of 1350-D. The other two lines were produced to ASTM Specification C-361, B-25 and C-25 designs, running for 3,891 and 678 ft, respectively. A twin run of 108-in. RCP Class 5 bore traveled 114 ft under a railroad track.

The city of Omaha is the project owner. Phase 1 was completed in June 2013, while the entire project is scheduled for completion in 2027. 

Download: Here