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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 NextDoor.com 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 purpose of the Underground Flow Equalization System is to help eliminate sewer overflows to San Mateo streets, creeks, the lagoon, and San Francisco Bay. These sewer overflows occur primarily during heavy rains, when additional water gets into the sewer system and overwhelms its capacity to transport wastewater to the treatment plant. Additionally, during peak rains, the wastewater treatment plant cannot treat the volume of combined excess water and wastewater it receives as quickly as it is entering the system.

In 2009, the San Francisco Bay Regional Water Quality Control Board (RWQCB) issued a Cease & Desist Order that requires the City to eliminate sewer overflows and provide capacity assurance. The permit that allows us to discharge treated water to the San Francisco Bay (which is the Environmental Protection Agency [EPA] 2013 National Pollutant Discharge Elimination System permit) requires us to eliminate blending and use an integrated approach to collect and treat the combined wastewater.

The Underground Flow Equalization System will allow us to temporarily divert excess volumes of wet weather wastewater flows (during heavy rains) until the collection system and the wastewater treatment plant have the capacity to accept the extra wastewater for conveyance and treatment. This will help the City comply with the RWQCB’s and EPA’s regulations. The System will also help when the City needs to conduct maintenance on the collection system by allowing workers to temporarily divert flows into the structure to facilitate sewer construction projects and operations and maintenance activities, such as pipeline inspection and cleaning.

The Underground Flow Equalization System will be an additional component of the wastewater collection system to provide increased wastewater holding during wet weather and sewer system maintenance. All components of the wastewater collection system ultimately feed into the wastewater treatment plant.

During heavy rains, the Underground Flow Equalization System will allow us to temporarily divert excess volumes of diluted wastewater into an underground concrete holding structure for up to approximately 24 hours, until the downstream collection system and the wastewater treatment plant have sufficient capacity to accept the excess wastewater for appropriate conveyance and treatment.  An underground pump station inside the holding structure will pump the wastewater back into the wastewater collection system for it to flow to the treatment plant.

Once the system is emptied, self-cleaning mechanisms will flush and clean the system, all while odor control systems are in continuous operation to prevent odors from affecting the surrounding community.

During dry weather, portions of the system may be used for temporary holding of wastewater for operations and maintenance activities. After any use, the system’s self-cleaning mechanisms will flush and clean the system.

Some minor fixtures, including access hatches, an electrical building, and vents for treated air, would be at or above the ground surface.

To meet the sewer overflow reduction goals, the Underground Flow Equalization System must be sized to accommodate approximately 5.3 million gallons. Approximate perimeter dimensions for the underground facility are 200 feet by 150 feet. These approximate dimensions will change and detailed dimensioning of the system will continue to be defined as the design progresses.

San Mateo does not currently have an Underground Flow Equalization System; however, these facilities are becoming more widely used across the entire country as a means of providing additional capacity in the system during heavy rains to help prevent sewer overflows. Daly City has been operating a similar system as part of its award-winning wastewater treatment system since 1989, and the city of Pacifica is in the process of constructing a similar equalization basin.

The 2014 Integrated Wastewater Master Plan and the 2016 Clean Water Program Final Programmatic Environmental Impact Report (Final PEIR) identified a total of 55 site alternatives, based on properties with potential sufficient space. These included municipal properties, schools, undeveloped property, private property, and parking lots. The Final PEIR also indicated a shortlist of 12 alternatives based on hydraulic modeling and beneficial impacts on addressing the City’s sewer overflows.

The shortlisted alternatives were evaluated based on technical requirements such as hydraulics, constructability, right-of-way, parking, and storage capacity. Five alternatives were rated highest from the technical analysis, and were further evaluated against non-economic criteria (such as social and environmental) and economic criteria (construction cost, operation and maintenance cost, easement and usage fee costs, and life-cycle costs). The non-economic criteria score and cost were determined for each site and a comparison of pros and cons was completed.

To inform the project team and policymakers, seventeen meetings with the public were conducted between August through December 2016, including Community Open House meetings, Public Works Commission, Parks & Recreation Commission, and meetings with several homeowner associations, to discuss the process, purpose, gather community input, and identify key issues. The feedback received at these meetings was incorporated into the Alternatives Analysis.

The results of the Alternatives Analysis were presented to the Public Works Commission in December 2016 and to the City Council in January 2017. The Commission and the Council screened the five alternatives and identified 1) the Corporation Yard and 2) San Mateo County Event Center as their preferred two alternatives to progress to the next steps of design and to be further evaluated. To view the December 2016 presentation, click here. To view the January 2017 presentation, click here.

The two preferred alternatives’ conceptual layouts were optimized for each site, required permanent and temporary construction easements were determined, and site restoration concepts were identified. A Phase 1 Environmental Site Assessment and California Environmental Quality Act initial studies were also performed, and the construction schedule and cost estimate for each site were updated.

In June 2017, staff presented the alternatives evaluation to the Public Works Commission and received recommendation for a final selection. Staff presented the same evaluations, plus the recommendation of the Commission, to the City Council on July 17, 2017, and received direction from Council on the final site to proceed through final design with the San Mateo County Event Center alternative. To view the July 2017 presentation, click here.

Since the Event Center location was selected, the City has worked with Event Center staff to determine feasible locations that are compatible with or present less disruption to Event Center activities. Out of three locations considered, the southwest corner of the parking lot was determined to be most feasible.

The City, as lead agency under the California Environmental Quality Act, is now proceeding with an Environmental Impact Report (EIR) for the project, which will tier from the previously certified 2016 Final PEIR and provide a project-level review of environmental impacts. To view the Final PEIR, click here.

Prior to preparing the Draft EIR, the City conducted a 40-day public scoping effort to solicit comments on the scope of the EIR. The Notice of Preparation was issued on September 7, 2018, and the scoping period ran from September 10, 2018 through October 22, 2018.

The Draft EIR is now available for public review and comment here. Hard copies are also available at City Hall, and the San Mateo Main and Hillsdale Library branches.

Public comments on the Draft EIR can be submitted through May 7, 2019.

How to submit comments:

  1. Write to: City of San Mateo Public Works Engineering, 330 W. 20th Avenue, San Mateo, CA 94403, Attention: Clean Water Program
  2. Email: info@CleanWaterProgramSanMateo.org
  3. Speak at: April 9 Planning Commission meeting, 7:00 p.m. at City Council Chambers, 330 W. 20th Avenue, San Mateo

A public meeting to receive comments on the Draft EIR will be held during the Planning Commission meeting on April 9, 2019.

During the 40-day scoping process that will start in late summer 2018, interested parties will have the opportunity to provide input and ask questions. A draft EIR is expected to be released in late 2018. There will be a 60-day public review and comment period. A Final EIR is expected to be released in late spring 2019, and will incorporate written responses to comments received on the Draft EIR. The Final EIR will be presented to the Planning Commission and City Council before it is adopted. For more information about how to provide comments during the scoping period, click here.

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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