The Clean Water Program is a comprehensive plan to upgrade San Mateo’s wastewater collection system and wastewater treatment plant to provide reliable service for years to come. The wastewater treatment plant is owned by the Cities of San Mateo and Foster City/Estero Municipal Improvement District. The wastewater treatment plant also serves Crystal Springs County Sanitation District, a portion of unincorporated San Mateo County, and the southern portion of the Town of Hillsborough. Those services are paid for by partner agency reimbursements.

The Clean Water Program is intended to meet the following goals:

  • To replace aging pipes and facilities. Sewer pipes have an average lifespan of 50-60 years, and most of San Mateo’s sewer pipes were constructed between 1900 and 1960. The wastewater treatment plant has many components that are over 75 years old, and nearly half of the system is reaching the end of its useful life. Although it has been maintained and upgraded over the years, improvements to meet current and future operating requirements are needed.
  • To meet current and future regulatory requirements and increase system capacity during heavy rains. The regulatory environment that protects our community continues to change. We are responding to the current direction of regulators (the Regional   Water Quality Control Board) that require specific corrective actions to prevent sewer overflows during heavy rains, while planning for future regulations related to the quality of our treated wastewater.
  • To align with long-term sustainability goals. Improvements to the wastewater treatment plant and sewer collection system will protect public health and the health of San Francisco Bay. The higher-quality water will become a source of recycled water that can be reused for landscaping and other uses. Additionally, the solid waste can be turned into an alternative fuel source for City vehicles.

In San Mateo, wastewater from homes and businesses is collected via a system of pipes (sewer laterals and mains) and pump stations. The collection system includes about 234 miles of pipelines, more than 5,500 manholes, and 26 pump stations. The collection system transports the wastewater to the treatment plant. There, it undergoes a series of biological and physical treatment processes so that it is suitable for discharge into the San Francisco Bay. The plant treats an average of 12 million gallons per day during summer months; during heavy rains, the plant can receive up to 8 times greater than the average normal flows.

Illustration of damage to sewer system.

Because the system does not have the capacity to treat the extra wastewater during heavy rains, sometimes sanitary sewer overflows (SSOs) occur. An SSO is the result of high volumes of rainwater mixing with sewage and exceeding the system’s capacity to transport and treat it. The Regional Water Quality Control Board has issued the City with a Cease and Desist Order for SSOs.

Read Wastewater: The Basics to learn more about San Mateo’s sewer collection system and Wastewater Treatment Plant!

Failure to meet our permit obligations (i.e., treating the discharged water to an acceptable quality) and Regional Water Quality Control Board requirements (e.g., preventing sewer overflows) by mandated deadlines could result in large fines that will be passed on to ratepayers.

The program is funded by sewer use fees paid by all properties that tie into the sewer collection system. The City is seeking grants and low-interest loans to finance the capital improvements needed, while minimizing the impacts on sewer rates.

Several communication channels are used to inform the public of new information and upcoming meetings. These channels include mailing of community meeting invitations, sending invitations to City Council and Boards/Commissions, and updating the City’s events calendar and Clean Water Program website. Additionally, the City emails residents, Homeowners Associations, and other community groups; posts to social media sites, such as NextDoor, Facebook, Twitter, and YouTube; and distributes press releases to various media contacts. The Program will continue to send community information through these channels, and the City encourages the public to subscribe to the email list and to to stay up to date with City and Program activities.

The Clean Water Program is a comprehensive plan to upgrade San Mateo’s wastewater collection system and wastewater treatment plant to benefit and protect the public and environmental health of the communities served – San Mateo, Foster City, Crystal Springs County Sanitation District, a portion of unincorporated San Mateo County, and a portion of the Town of Hillsborough. The improvements at the wastewater treatment plant are intended to replace aging infrastructure, meet current and future regulatory requirements, increase system capacity during heavy rains, and align with long-term sustainability goals to provide reliable service for years to come.

The regulatory environment that protects our communities continues to change.  Not completing the capital improvements will lead to the City of San Mateo, and its regional partner agencies, failing to comply with the Regional Water Quality Control Board’s Cease and Desist Order and the National Pollutant Discharge Elimination System permit requirements. Failure to comply with cease and desist order and permit requirements, by mandated deadlines, could result in large fines that will be passed on to ratepayers. Our infrastructure will continue to deteriorate and will continue to have failures. These failures include sanitary sewer overflows that leak diluted raw sewage and pollutants onto our communities’ streets and into our creeks, beaches, lagoon, and the San Francisco Bay. During heavy rains, the wastewater treatment plant can be overwhelmed and must blend, or partially treat, the wastewater, which does not meet current and future regulatory discharge permit requirements. Sanitary sewer overflows and blending at the treatment plant are significant health concerns that negatively impact the community and the environment.

One of the objectives of the Clean Water Program is to align with long-term sustainability goals. The design for the wastewater treatment plant will pursue LEED Silver Certification  for the new Administration Building and follow ENVISION guidelines for sustainable infrastructure for the overall project where appropriate.

The wastewater treatment plant improvements will be constructed on the adjacent parcel north of the existing treatment plant. The existing plant must remain in operation while the new plant is constructed. When construction is completed, the solids handling facilities on the existing site will be integrated with the new improvements, and the liquid processing facilities that are no longer needed will be demolished or repurposed.

Aerial view of the WWTP footprint

Major construction is anticipated to begin in summer 2019, once the required permits are obtained. Minor activities, such as clearing the site of vegetation, will begin earlier.

Major construction is expected to begin in the summer of 2019 and be completed in five years. The overall project will consist of site preparation, major construction, testing, startup, and commissioning.

Applicable Bay Area Air Quality Management District emission control measures will be implemented during construction to mitigate dust generation. The details of the emission control measures will continue to develop as the design progresses. Approved work hours for construction activities and best practices will be employed to reduce sound levels from construction activities as much as practical. Notification protocols will be established to notify the surrounding neighborhood of construction activities, times, and contact information.

Best practices will continue to be employed by the wastewater treatment plant staff during construction to continue efficient operation of the existing odor control systems. The new wastewater treatment plant facilities are being designed with odor control systems that meet or exceed the efficiency of the systems currently in place and therefore future odor generation is expected to decrease compared to current conditions.

The wastewater treatment plant construction site will be fenced where necessary to provide security and public safety.

The Clean Water Program will prepare and implement a traffic management plan to minimize the impacts of construction activities on traffic and public access to recreational facilities. The details of the traffic management plan will continue to develop as the design progresses. Any truck routes established in the future traffic management plan will comply with “Chapter 11 – Vehicles and Traffic” of the City’s Municipal Code.

A traffic management plan will be prepared and implemented to minimize the impacts of construction activities on vehicular, pedestrian, and bicycle access to nearby parks and the Bay Trail. Various routes may be developed to provide temporary and permanent access to the parks and Bay Trail both during and after construction. A permanent pedestrian and bicycle access route around the wastewater treatment plant is being considered to allow pedestrians and bicyclists to cross between the east and west ends of the plant.

The Clean Water Program will prepare and implement a traffic management plan to minimize the impacts of construction activities to pedestrians. Potential impacts to adjacent schools, residents, and businesses will be taken into consideration during the preparation of the traffic management plan as design progresses.

Preliminary planting image boards will be made available on the Clean Water Program’s website through the planning process. Final landscaping design and planting schedules will be developed later in the planning process.

Public outreach and transparency are important components of the Clean Water Program. The Clean Water Program staff hosts community meetings and reaches out to neighborhood and community organizations when important topics that affect the community need to be communicated. In addition, this website contains project documents, presentations, and videos posted to inform and educate the community. The Clean Water Program has established a telephone number for use by the public to report any conditions associated with construction.

The wastewater treatment plant is protected by an existing levee system that is operated and maintained by the City of San Mateo and the City of Foster City. As a secondary level of protection, the new facilities will be elevated to protect equipment and facilities by incorporating a 3-foot water surface elevation increase over the Base Flood Elevation, based on projected sea level rise for the Year 2100.

The increase in rates was established to fund the Clean Water Program, which is a $900 million capital improvement program to upgrade San Mateo’s wastewater collection system and the San Mateo Wastewater Treatment Plant. The City has approved a sewer rate restructure to incorporate a fixed fee component, plus a multi-year rate adjustment to improve the stability and predictability of sewer revenues needed to fund the improvements.

The wastewater treatment plant is owned by the Cities of San Mateo and Foster City/Estero Municipal Improvement District. Capital improvements at the wastewater treatment plant are paid for by both owners, based on their ownership distribution of the new improvements. The wastewater treatment plant also treats wastewater for Crystal Springs County Sanitation District, a portion of unincorporated San Mateo County, and the southern portion of the Town of Hillsborough. Those customer agencies pay for the sewer services the City of San Mateo provides.

The height of the upgraded and expanded facilities will be no taller than the existing digesters, which are the egg-shaped structures and the tallest facilities on the existing plant. The new facilities will comply with maximum height limitations per the City of San Mateo General Plan and Municipal Code.  Below is a conceptual rendering of the new facilities. (NOTE: This rendering is subject to change as the design process progresses.)

Wastewater Treatment Plant Conceptual Rendering

The Clean Water Program is a comprehensive Capital Improvement Program that, in addition to the wastewater treatment plant project, includes various collection system pipe improvements throughout San Mateo. For example, projects are planned for Dale Avenue and near the Dale Avenue Pump Station. The exhibit below illustrates the collection system improvement locations.

Map of runoff basins in the San Mateo project area.

The Underground Flow Equalization System (UFES) project consists of:

  • An underground, concrete holding structure capable of temporarily storing up to 5.3 million gallons of wastewater. It is located in the east corner of the Event Center property. The facility is 200 feet by 150 feet, and 35 to 50 feet deep. Access hatches and manhole covers will be visible.
  • Above ground electrical building
  • Diversion System (diversion sewers, diversion structure, and force main) that routes wet weather flows to and from the existing Delaware sewer trunk line
  • Odor Control System will continuously clean the air and vent the facility.
  • During heavy rains, the Delaware sewer trunk line and other areas in the system reach capacity and cause sanitary sewer overflows (SSOs). The UFES will temporarily route diluted wastewater flows from the Delaware trunk line to the underground holding structure, where it can be stored for up to 24 hours.
  • Once the downstream collection system and WWTP has available capacity, a pump station inside the holding structure will pump the wastewater back into the collection system.
  • The facility can also be used to support operations and maintenance activities in other areas of the system, such as pipeline inspection and cleaning.
  • After any use, self-cleaning mechanisms will flush and clean the facility. The interior is inspected after every event.
  • Odor control systems will operate 24/7.
  • The facility is expected to be used less than 20 times per year on average.
  • During heavy rains, San Mateo’s sewer system capacity is overwhelmed and causes SSOs that impact the health of the community, creeks, beaches, lagoon, and San Francisco Bay.
  • In 2009, the San Francisco Bay Regional Water Quality Control Board (RWQCB) issued a Cease & Desist Order that requires the City to eliminate SSOs.
  • Many of these SSOs occur on Delaware Street and contaminate Borel Creek, which flows through the Fiesta Gardens neighborhood.
  • In conjunction with the other Clean Water Program improvements, the UFES enables the City to prevent SSOs from occurring and comply with State and Federal regulations.
  • Staff initially evaluated 55 sites throughout the City to potentially locate UFES. As part of the evaluation process, City staff and members of the Council visited several underground flow equalization facilities in Seattle, Washington. These facilities were located underneath parks and parking lots, and were adjacent to various residential, school, and commercial properties. Based on the information learned from the Seattle systems, parks at Bay Meadows and Fiesta Gardens were determined to be preferred locations for UFES. However, due to opposition to these locations from local residents, staff focused on further evaluating the City’s Corporation Yard and the County Event Center as potential sites.
  • After further evaluation, the County Event Center Corner site was preferred over the Corporation Yard due to various factors (such as impacts to operations, proximity to residents, permitting requirements, and longer construction schedule). Because the Corporation Yard is the essential hub for the City’s Public Works and Parks and Recreation operations, staff would have to be relocated for the duration of the UFES project. However, the City was unable to find suitable temporary sites for the operations. Additionally, there were zoning restrictions on the Corporation Yard.
  • The County Event Center site offered a shorter construction schedule and a less complex permitting process. Initially, the City identified the three corners (northwestern, southern, and eastern corners) of the County Event Center. Because the northwestern and southern corners presented challenging conditions for the operations of the Event Center, these were eliminated from further consideration. As a result, the Event Center staff determined that the eastern corner would be preferred and agreed to negotiate an easement for the location of the UFES project.

Construction of the 5.3 MG underground structure will be done in six phases: site preparation, shoring installation, excavation, micro-pile installation, concrete, and site finishing. Construction is anticipated to take approximately 25 months, with some of the phases overlapping. The diversion system will be constructed concurrently.

Phase 1: Site Preparation
  • During this phase, the site will be cleared, construction trailers and equipment will be brought to the site, construction fencing will be installed, and dust control measures will be in place.
  • At this time, equipment to monitor groundwater, vibration, and settlement will be installed.
  • This phase is expected to take approximately 3 months.
Phase 2: Shoring Installation and Dewatering
  • The shoring system will safely hold the area open during excavation. During this phase, shoring construction equipment will be brought to the site. The contractor will select one of three low vibration and noise systems for the installation of the shoring system. It is important to note that no sheet piles will be used on this project.
  • Once the shoring equipment is installed, groundwater will be pumped out of the work area. The soil and groundwater have been tested to confirm there is no contamination. Additionally, dewatering tests were performed to observe groundwater level fluctuations in nearby wells. Water will be removed (dewatering) from inside the shoring to maintain stability. This dewatering method will not cause the groundwater levels to change from typical conditions beyond the property line.
  • The City will survey and document nearby structures before, during, and after construction. During construction, the City will monitor groundwater levels, noise, and vibration. Enforceable thresholds will be set and enforced, where work can be stopped if work exceeds the specified limits.
  • This work is expected to take approximately 4 months.
Phase 3: Excavation
  • Once the shoring is complete, excavation will begin and the soil inside the shoring will be removed. During this phase, the City will monitor groundwater, vibration, and noise levels. Dust control measures will be in place.
  • This work is expected to take approximately 3 months.
Phase 4: Foundation Micro-Pile Installation
  • A network of foundation piles will be drilled to prevent uplift (floating) from the high groundwater levels, to support the structure and to keep it in place during seismic events. Seven different pile types and installation methods were evaluated. Micro-piles were selected because they meet the technical requirements, while being quieter and having less vibration than other methods. During this phase, approximately 270 micro-piles will be installed. The City will continue to monitor for groundwater levels, vibration and noise.
  • This work is expected to take approximately 2 months.
Phase 5: Concrete
  • In Phase 5, the concrete base, walls, column, beams, and roof elements of the UFES structure will be built. Concrete trucks and pumping equipment will be on site.
  • The City will continue to monitor for groundwater, vibration, and noise throughout this phase.
  • The duration of this work is expected to be 9 months.
Phase 6: Site Finishing
  • Once the concrete is done, the new electrical building will be installed, in addition to new plantings and fencing along Saratoga Drive and new pavement. The permanent, active odor control facility will be installed (on the far west portion of the site, away from the park). The remainder of the site will be repaved and restored to Event Center usage.
  • The construction crews will be demobilized, and the new facility will undergo startup and testing.
  • The City will continue to monitor for groundwater, vibration, and noise throughout this phase.
  • The duration of this work is expected to be 8 months.

  • Work may take place from 7 am to 7 pm, which is allowable per City ordinance, with most construction activities only requiring 8-10 hours per day.
  • Weekend and evening construction is not allowed. However, exceptions may be needed for certain activities, such as concrete pours. City approval and notice to the surrounding community would be required for this.

Yes. There will be a live response for citizen inquiries and a dedicated phone number.

The UFES project footprint is about 32,000 sf. The 400/450 Concar development has an approximate footprint of 134,000 sf. The SurveyMonkey building is approximately 87,000 sf. Both buildings had similarly deep excavations for their underground parking.

  • The City will require construction noise to comply within the City’s noise ordinance.
  • The City has eliminated impact pile driving and is now using a quiet pile alternative called “micropiling” that generates one-quarter the amount of noise.
  • Piling will be installed 50 feet below ground surface and will require approximately 6 to 8 weeks to complete.
  • The City is currently developing a monitoring plan which includes noise monitoring devices in the vicinity of the work. The final noise monitoring plan will be posted to the Program website once complete. The City will enforce noise violations through their independent construction manager who will be onsite during any work activity.
  • Dust control will meet or exceed regulatory requirements.
  • Dust will be visually monitored per Bay Area Air Quality Management District permit requirements for construction dust particulate compliance needs.
  • Measures will be taken by the contractor, such as wet sweeping on surrounding streets and around the construction site, covered trucks, site watering, fence screening and tire wash facilities.
  • The City’s construction manager will enforce the dust prevention measures and compliance with regulatory requirements.
  • A soil investigation was performed for the project and no contamination of the soil or groundwater was found.
  • The UFES project will utilize a shoring system that acts as a cutoff wall during construction and that prevents groundwater from entering the excavation and isolates the excavation from the surrounding groundwater. This creates a closed “bathtub” effect, allowing work to proceed inside the structure without impacting the surrounding groundwater table and eliminating soil instability and settlement nearby.
  • The City has conducted a geotechnical evaluation for the project to help develop prevention measures for settlement. The results showed that groundwater is 3’-5’ below ground, no contamination was found in the soil or groundwater and historical baselines of groundwater level fluctuations were obtained in wells installed around the site. Based on the subsurface conditions, the following measures will be taken to ensure settlement does not occur:
    • Additional observation wells will be installed near the site before construction to monitor and establish baseline groundwater level measurements.
    • Dewatering wells will be placed within the cutoff wall, and will be prohibited from being placed outside the excavation (this significantly reduces the potential for settlement).
    • Dewatering drawdown will be minimized to 2’ below the excavation.
    • The groundwater cutoff wall will extend at least 15’ below the excavation and watertight shoring will be required.
    • Enforceable drawdown stop-action thresholds and corrective actions will be required.
    • Groundwater levels will be measured during and after construction and compared to the baseline measurements.
    • Existing structures will be surveyed and documented before, during and after. construction to differentiate between construction related impacts and pre-existing conditions (which houses in the area to survey is currently being evaluated).
  • By implementing the actions above, the results will lead to a proven groundwater dewatering approach that will minimize the groundwater “cone of influence” to less than 10 ft. from the edge of the UFES basin. This will significantly reduce the potential issues that sometimes impact surrounding community structures.
  • Vibration monitoring will occur during the use of heavy equipment. The Contract Documents will specify maximum vibration limits and enforceable actions if they are exceeded. The City is currently developing a monitoring plan which include vibration monitoring devices in the vicinity of the work. The details of this plan, including how it will be enforced and by whom, will be made available when completed. However, vibration is not anticipated to be a significant impact to the project with both driven sheet piles and driven foundation piles being excluded from consideration.
  • The contractor will be required to submit an overall traffic management plan that must have City review and approval.
  • The plan will attempt to minimize the traffic impacts to the surrounding community as much as possible.
  • Construction from the project site is planned to be routed along Saratoga Dr. to the nearest designated and approved City truck haul routes: Delaware St. or Hillsdale Blvd.
  • Lanes on Saratoga and Delaware St. will need to be closed for some of the work, but it is not anticipated that entire roads will be closed.
  • This project is estimated to add an average of 120 vehicles per day over the entire project or about 10 additional vehicles per hour. For comparison, over 800 vehicles per hour use Saratoga Dr. (northbound and southbound) during the afternoon peak.
  • The City will continue to evaluate alternate routes and traffic control options and will coordinate with other construction projects in the area.
As part of the traffic management plan that will be required of the contractor and reviewed by the City, the plan will provide safe pathways for pedestrians and bicyclists attempting to navigate by the construction area.
  • The force main along Saratoga Dr., from the 5.3 MG underground structure to Delaware St., will be constructed using trenchless methods for most of the alignment. Majority of the work will be pipe lining an existing 18” sewer pipe. A portion of the work to install a segment of new 18” sewer pipe will utilize a trenchless method called horizontal direction drilling.
  • The 36” gravity diversion sewer will be installed by open cut methods. The design team previously looked at the possibility of microtunneling for this pipeline, but the tight curve of Saratoga Drive raised significant constructability, cost and schedule impacts.
  • The City has been using open cut trenching throughout the City for many decades and is currently using open cut to numerous sewer projects throughout the City.
The draft EIR discusses specific environmental requirements for wildlife protection. For example, Mitigation Measure 5-2 requires biological surveys prior to construction to ensure the protection of any native bird nests and the establishment of protective buffers based on standards established by the California Department of Fish and Wildlife.
Yes. These details have yet to be worked out, but the City is interested in creating opportunities for the community to learn about and see the project during construction.
  • The odor control system will continuously operate and will dry out the interior after usage
  • Proven carbon scrubbing technology will be utilized, similar to the UFES projects the Council visited in the Seattle area in 2016.
  • After each usage, the underground structure will be automatically pumped out and flushed clean with water, which will remove material that could cause odors.
  • The City, as lead agency under the California Environmental Quality Act (CEQA), has prepared an Environmental Impact Report (EIR) for the UFES Project. The Draft EIR provides a project-level review of potential environmental impacts from the project. The draft EIR is no longer available for public review and comment. However, there will be additional opportunity for comment on the Final EIR when it is made available.
  • For other inquiries, the public can call the hotline, 650-727-6870, or email
  • The Draft EIR public comment period closed on May 31. The Clean Water Program team has logged all submitted comments/questions and provided response with acknowledgements of receipt and indicated that all comments/questions would be addressed in the Final EIR.
  • The project’s next community engagements will be at a Planning Commission Study Session on August 27.
  • For the certification and adoption of the project’s Final EIR and approval of the special use permit, the project will return to the Planning Commission on September 24, then the City Council on October 7, 2019.
  • Construction is anticipated to begin in Spring 2020 and last until Fall 2022.

The final design is required to meet seismic safety thresholds and standard building codes. The system will be designed to withstand the U.S. Geological Survey seismic acceleration of 1.9 g, which is specific to San Mateo. The design will also comply with governing codes, such as Reinforced Concrete ACI 350, California Building Code 2013, and Design Loads for Buildings and Other Structures (ASCE 7-10).

Taxes are not used to pay for this project or any of the City’s sewer projects. All City-supported wastewater related activities, including conveyance, treatment, maintenance, operation, repair, upgrades, and replacements are funded by sewer fees paid by property owners in San Mateo and through cost-sharing contributions from partner agencies, including the City of Foster City, Town of Hillsborough, County of San Mateo, and Crystal Springs County Sanitation District. The City has approved increases in sewer rates from Fiscal Year 2017/18 through 2022/23 to fund sewer operations and maintenance and clean water improvement activities. The City is also seeking funding options such as grants and low-interest rate loans to minimize the impact of this multi-year capital improvement program on sewer rates.

Geotechnical soil investigations have been completed as part of the design. Construction of the system will require soil excavation, and shoring will be utilized to maintain the integrity of the excavation.

Please visit the City of San Mateo’s updated sewer rate page here.

To see the administrative regulations page, please click here.

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