Primary Sedimentation Tank Rehabilitation and Electrical Upgrade
- Project typeSystem Improvements
- Project value$16.9 million
Project Overview
The Regional Water Quality Control Plant was initially constructed in 1934 and has undergone several expansions and upgrades, including constructing the primary sedimentation tanks (PSTs) in 1972. The four concrete PSTs (each measuring 220 feet long by 41 feet wide by 14 feet deep) are covered with a monolithic concrete slab and equipped with mechanical and electrical equipment for wastewater flow control along with sludge and scum removal. Over the course of their 52-year life, the original corrosion protective coating on the interior of the PSTs failed, causing concrete deterioration (e.g., cracks and spalling concrete) on the interior surfaces of the tanks. Most of the PSTs' original equipment has reached the end of its useful life.
Rehabilitating the PSTs and their ancillary systems is necessary to ensure reliability for continuous use of the primary treatment units and to ensure compliance with current and future regulations. This project will restore the structural integrity and extend the life of the tanks by 30 years while avoiding complete replacement. This preserves capital resources for other uses.
Construction funding has been secured for this project via a low-interest, 30-year Clean Water State Revolving Fund (SRF) loan. Eighteen percent of the construction work was completed by Disadvantaged Business Enterprise (DBE) subcontractors. The annual SRF loan repayment, which includes principal and interest, will begin in December 2025 based on an amortized period of 30 years. The Plant's partner agencies will share in the repayment of the loan.
This project was identified in the Long-Range Facility Plan (LRFP) which was completed in 2012.
Scope of Work
- Remove corroded rebar and spalling concrete from the tank structure. Install replacement rebar and perform concrete repair to restore the structural integrity of the tanks and their concrete covers
- Apply corrosion protective coating on the interior of four concrete tanks at locations above the normal water table where sewer off gases accumulate
- Upgrade electrical, instrumentation, and controls associated with operating the primary sedimentation tanks’ sludge raking mechanism and ancillary process units
- Install a pre-engineered metal building to house new power distribution equipment to meet current National Electrical Code (NEC)
Public Impact
There were no public impacts.
Environmental Impact
During construction, impacts to the environment were minimized. For example, all spent washwater generated from cleaning the concrete tank and deck were collected and returned to the plant’s headworks for treatment. Most of the work took place inside the tanks and on the tank covers. The new electrical building was installed on an already improved area inside the plant. Impacts to wildlife were minimal.
Project Milestones
- 2012 – Project was identified in the Long-Range Facility Plan (LRFP)
- 2018 to 2019 – Selected design consultant and completed the design
- 2021 to 2023 – Procured SRF Loan. Awarded construction and construction management contracts
- January 2025 – Construction completed
Project Documents
Long Range Facility Plan Final Report August 2012.pdf(PDF, 41MB)
Project Completion Report Primary Sedimentation Tanks.pdf(PDF, 2MB)
Primary Sedimentation Tanks and Electrical Upgrades before-and-after-photos.pdf(PDF, 736KB)
Project Location
2501 Embarcadero Way
