Richmond Wet Weather Storage Facility Design-Build (CA)


The City of Richmond is located 16 miles northeast of San Francisco, directly across San Francisco Bay. With 32 miles of shore, the city’s total area is 56 square miles, of which 34 are land and 22 are water areas. The city’s wastewater treatment plant is operated and maintained through the Water Resource Recovery Department.

The City of Richmond entered into a legal settlement with the San Francisco Bay Keepers to prevent possible wet weather overflows from its collection system into the San Francisco Bay. Built in the 1940s, the wastewater treatment plant did not have the hydraulic capacity to handle wet weather event flows, causing surcharging of the collection system. When originally constructed, the collection system included a number of SSOs to manage wet weather events. Over the years, record-keeping of “as-builts” of the sewer collection was inconsistent, and the condition of many parts of the collection system were unknown. Several challenges faced the City:

  • The Bay Keeper’s settlement included large penalties for not meeting a difficult schedule.
  • The main sewer influent pipe was believed to be approximately 50 feet below grade beneath poor bay peat type soils.
  • Operations of the plant could not be impeded during new construction.
  • The system is planned to operate just 7-10 times per year.
  • There were significant local and minority business requirements that needed to be incorporated into the procurement.


Due to the schedule constraint and the desire to have input on design elements, the City elected to use a collaborative delivery approach. Carollo Engineers designed and constructed a wet weather storage system that would be tied in to the main plant influent line just upstream from the wastewater treatment plant. The project included a 40-mgd pump station, a 5-million-gallon concrete storage tank, and 1,500 lineal feet of dual-purpose pipe. During wet weather events a portion of the influent is diverted to the storage tank to handle the flow peaks. Following the wet weather event, the diverted wastewater flows in the opposite direction back into the collection system. To avoid odors, the inside of the storage tank is automatically rinsed, and the entire system is connected to a bio filter. The pipeline had to be buried beneath an active commercial nursery. As such, the pipeline had to be installed during a very short “non-growing season” window.


The project was completed in 17 months, one month ahead of schedule, without hindering plant operations and prior to the court-mandated completion date. Work in the nursery was completed within the allowed time frame as well. The project also came in under budget while meeting the City’s local hire and local business enterprise goals. The system has been in operation since 2015 and has worked flawlessly through each wet weather event since.