Improvements to the Main Sanitary Sewer Line

With construction beginning in 2023, the City of Boulder will be embarking on an improvements project for the main sanitary sewer line which carries the majority (90%) of the city's wastewater collection to the Boulder Water Resource Recovery Facility.

  1. Plan

  2. Community Engagement

  3. Design

  4. Implement

Current Phase

Project Overview

The city owns and operates approximately 360 miles of sanitary sewer that comprises its wastewater collection system. In 2016, the city completed its Wastewater Collection System Master Plan (WWCSMP). One of the outcomes of the plan was the identification of vulnerabilities within the system. The plan determined that the city’s wastewater collection system generally has adequate capacity to convey dry weather flows to the Boulder Water Resource Recovery Facility (WRRF). However, during significant rainfall events, the collection system can become hydraulically overloaded with the introduction of inflow and infiltration (I&I) to the system. The WWCSMP identified several sanitary sewer sections that lack capacity under these wet weather conditions. The main sewer improvements project was one of four top priority projects identified in the WWCSMP where the sewer system lacks capacity during wet weather conditions.


Current Phase: The project is currently in the final design phase and is anticipated to begin construction early 2023.

Detailed Facts: The project will:

  • Strengthen wastewater infrastructure by rehabilitating the existing pipeline (which is at the end of its service life and is heavily corroded).
  • Protect public health by increasing wastewater conveyance capacity by constructing a new section of pipeline from Valmont Road down to the WRRF which will reduce sanitary sewer backups and wastewater manhole surcharges.
  • Reduce flood vulnerability by moving most wastewater flow out of the floodway.
  • Conserve the environment by decreasing the risk of wastewater discharge into the environment, by selecting already-impacted areas for the new pipeline alignment, and by using trenchless rehabilitation technologies for the existing pipeline.

Estimated Cost: $50M

Funding: This project is being funded through utility fees

Project Impacts

Throughout this project, community members should expect to experience traffic impacts along Valmont and 61st Streets. Community members should also expect to experience temporary closures of sections of Sawhill Ponds and Walden Ponds trails. Please check the city's Cone Zones for current traffic impacts, the city's trail closures webpage for impacts to Sawhill Ponds trails, and Boulder County's trail closures webpage for impacts to Walden Ponds trails.

Some access points to properties adjacent to the project will experience impacts. The project team will reach out to affected property owners prior to construction commencing to work with them on individual access solutions.


This project is located north of Valmont Road between 57th St. and 75th St.