Underhill Combined Sewer Overflow (34-2) Storage Facility

  • Underhill Combined Sewer Overflow (34-2) Storage Facility
  • Underhill Combined Sewer Overflow (34-2) Storage Facility
  • Underhill Combined Sewer Overflow (34-2) Storage Facility

Underhill Combined Sewer Overflow (34-2) Storage Facility

Spokane, WA
Customer: City of Spokane
Date Completed: September 2015

The Underhill Combined Sewer Overflow (34-2) Storage Facility & Freya-Thor Trunk project was a $7.8M project constructed for the City of Spokane starting in March 2014, and completed September 2015. The project included construction of a 1,430,000-gallon cast-in-place concrete storage tank and flow control facility, approximately 4,100 linear feet of combined sanitary and storm sewer piping, and associated civil work for street and landscape restoration.


The storage tank was approximately 375 feet long by 105 feet wide with wall heights nearing 20 feet. It incorporated over 6,000 CY of structural reinforced concrete, 38 roof hatches and manholes, and extensive mechanical and electrical equipment for flow and odor control. The associated piping primarily consisted of 36”, 48”, and 54” diameter reinforced concrete pipe. The tank site is located within an active city park, so community outreach and public relations were critical.


This project was a recipient of the Associated General Contractors NW Build award, 2016.