Underground Flow Equalization System
Current Underground Flow Equalization System Progress
Below are a live view from our construction site camera and a 3D visualization of the current phase of the project. In order to start the live camera view, click on the three lines symbol and click the LIVE button. The video will load in a few seconds. This page is best viewed with the Chrome browser and may not be fully functional with Internet Explorer.
Please click here for the recording of the UFES Virtual Community Meeting from Dec. 21, 2020. The project and construction team provide details of the project and answer questions from the community.
Construction Camera
Visualization of current project phase
What Is the Underground Flow Equalization System and Why Is It Important?
The City of San Mateo is currently under a Cease and Desist Order issued by the Regional Water Quality Control Board to eliminate sanitary sewer overflows (SSOs). SSOs occur primarily during heavy rains, when excess water enters the sewer collection system and overwhelms its capacity. During these events, sewage flows out of the system onto the City’s streets. The Underground Flow Equalization System (UFES) consists of an underground 5.3-million-gallon structure that will help eliminate SSOs in San Mateo and comply with the Cease and Desist Order.
A Proven Technology
These facilities are becoming more widely used across the entire country to provide additional capacity in sewer systems during heavy rains to help prevent sewer overflows. Seattle, Sacramento, Pacifica, and Daly City use them.
Project Schedule
Due to the scale and complexity, the UFES project will be constructed in 6 phases, with pipeline work occurring concurrently, over approximately three years. More information about the UFES project can be found here.
PHASE 1: SITE PREPARATION
Construction Start: July 2020
Construction Finish: Fall 2020
PHASE 2: SHORING
Construction Start: November 2020
Construction Finish: Winter 2021
PHASE 3: EXCAVATION
Construction Start: Early 2021
Construction Finish: Fall 2021
PHASE 4: MICROPILES
Construction Start: Fall 2021
Construction Finish: Winter 2022
PHASE 5: STRUCTURE (Concrete, Mechanical, Electrical)
Construction Start: Winter 2022
Construction Finish: Summer 2023
PHASE 6: SITE FINISHING
Construction Start: Winter 2022
Construction Finish: Fall 2024
Pipeline Construction in Saratoga Drive:
Construction Start: Winter 2020
Construction Finish: Winter 2023
Pipeline Construction in S. Delaware Street:
Construction Start: Fall 2021
Construction Finish: Summer 2024
Project Status
The Underground Flow Equalization System (UFES) Project is moving steadily towards completion. While some finishing touches are being completed, the main system has been operational since December 2023. Since then, we have experienced 4 major rain events, during which the system has temporarily held a total of approximately 8 million gallons of diluted wastewater. This is an early indication of the success of the system achieving the goal to significantly reduce the number of sewer system overflows in the San Mateo area.
Visualization of finished construction
The City’s contractor continues to demobilize from the site. Major traffic impacts related to the UFES project along S. Delaware Street have concluded, and are nearing completion on Saratoga Drive. Minor occasional traffic inconveniences will continue as the overall project progresses through the final site finishing activities.
The City has also discontinued dust and noise monitoring in the vicinity of the San Mateo County Event Center Site, another sign of significant progress towards project completion. Potential violations and resulting risks from construction-related dust and noise were a concern for many residents near the site at the start of construction; however, no significant construction-related concerns were observed during the monitoring timeframe.
The City anticipates that the UFES project in its entirety, including work at the San Mateo County Event Center, will conclude in early Summer 2024.
We thank you for your continued patience and cooperation as we make steady progress toward the completion of our sewer system improvements.
Approved work hours are as follows:
San Mateo County Event Center Site: 7 a.m. – 7 p.m.
Saratoga Drive: 7 a.m. – 5 p.m.
South Delaware Street: 7 a.m. – 5 p.m.
*Construction schedules and traffic patterns are subject to change.
Updated on April 2, 2024
Upcoming Work
UFES Project Substantially Complete
Our Underground Flow Equalization System (UFES) project has reached the milestone that our community has been eagerly awaiting – it is substantially complete! Remaining work is minimal and includes site cleanup, final pieces of performance equipment, removal of a temporary barrier at the new site entrance, and some minor landscape work around the project areas. The major accomplishment of the project is the 5.3-million-gallon UFES structure beneath the parking lot of the Event Center. Other than a small operations building, the entire structure and associated equipment is underground. The system operated successfully during preliminary tests during the last rainy season and is ready to minimize future sewer overflows.
We would like to extend our appreciation to our community for your continued patience and cooperation throughout the design and construction process.
Updated on September 4, 2024
Construction Monitoring
As part of our ongoing commitment to the community living and working near the UFES project, the City is providing live camera feeds to view the on-site activities, and is monitoring dust, noise, vibration, and groundwater levels for the duration of construction. Dust, noise, and vibration monitors are placed at the two project fence lines along Saratoga Ave and Bay Meadows Park. Groundwater monitoring wells are located on-site and in the surrounding neighborhoods. After the City completes a quality control review of the monitoring data, the City will post summarized monitoring updates below. The City will be utilizing best management practices to prevent dust, noise, vibration, and groundwater levels from exceeding the threshold levels; however, if threshold exceedances occur during the reporting timeframe, the City will report the causes and corrective actions taken.
NOISE
Project not to exceed 90 dBA at the property line at Saratoga Ave and Bay Meadows Park
Significant construction at the San Mateo County Event Center Site has ended and the excavation has been backfilled. The remaining work poses very little risk for generating excessive noise; therefore, noise monitoring ended 3/30/2024.
VIBRATION
Project not to exceed vibrations of 1.0 inches per second for more than 30 seconds
Dewatering operations at the San Mateo County Event Center Site have ended and the excavation has been backfilled. The remaining work poses very little risk for impacting vibration and settlement; therefore, vibration and settlement monitoring ended 11/19/2023.
DUST
Project not to exceed dust particulate levels of 82 pounds per day
Significant construction at the San Mateo County Event Center Site has ended and the excavation has been backfilled. The remaining work poses very little risk for generating excessive dust; therefore, dust monitoring ended 3/30/2024.
GROUNDWATER
Click link below for additional information
Dewatering operations at the San Mateo County Event Center Site have ended and the excavation has been backfilled. The remaining work poses very little risk for impacting groundwater levels; therefore, groundwater level monitoring ended 12/13/2023.
Where Will the UFES Be Located?
The UFES will be located on the San Mateo County Event Center property between Saratoga Drive and South Delaware Street. After an extensive site selection process, including more than 20 public meetings and hearings, the east corner of the Event Center parking lot was determined to be the most feasible location. Several presentations on UFES and the site selection process can be found on our Presentations page.
Representation of Site Preparation
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, dust, and noise will be installed. The City performed baseline assessments of properties neighboring the Event Center site to assess existing conditions and begin monitoring for settlement.
Phase 2: Shoring Installation
During this phase, shoring construction equipment will be brought to the site. The shoring system will safely hold the area open during excavation. The contractor has selected a low-vibration and low-noise system for the installation of the shoring system that has been approved by the City.
Once the shoring equipment is installed, groundwater will be pumped out of the work area to maintain stability of the excavation walls. This dewatering method should not cause the groundwater levels to change from typical conditions observed in recent groundwater level tests conducted beyond the Event Center property line. The groundwater has been tested to confirm there is no contamination.
During construction, the City will monitor groundwater levels, noise, dust, and vibration. Enforceable thresholds will be set and enforced, where work can be stopped if work exceeds the specified limits. The City will keep you informed of any exceedances and corrective actions taken.
The condition of properties assessed prior to construction will be re-assessed for settlement throughout the construction process.
Representation of Shoring Installation
The figures below show the effects of dewatering, and groundwater levels, in the Bay Meadows and Fiesta Gardens neighborhoods.
Controlling Groundwater in the Bay Meadows Neighborhood
Controlling Groundwater in the Fiesta Gardens Neighborhood
Representation of Excavation Work
Phase 3: Excavation
Once the shoring is complete, excavation will begin and the soil inside the shoring will be removed. The soil has been tested to ensure there is no contamination. Dust control measures will be in place.
The City will continue to keep you informed of any exceedances of dust, noise, vibration, and groundwater levels, and corrective actions taken.
Phase 4: Foundation Micro-Pile Installation
A network of foundation piles will be drilled to support the structure and prevent uplift (floating) from the naturally high groundwater levels, 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 vibrating less than other methods. Noise from the installation of the micro-piles is expected be below the City’s noise ordinance – this sets a level of 90 dBA at the property line. The City will monitor noise throughout the construction process and keep you informed of any exceedances and corrective actions taken.
Representation of Micro-Piles under UFES Structure
The figures below show the expected noise levels in the Bay Meadows and Fiesta Gardens neighborhoods during the installation of the micro-piles.
The City will continue to keep you informed of any exceedances of dust, noise, vibration, and groundwater levels, and corrective actions taken.
Section Showing Anticipated Sound Levels from Micropiling Activities in the Bay Meadows Neighborhood
Section Showing Anticipated Sound Levels from Micropiling Activities in the Fiesta Gardens Neighborhood
Representation of Phase 5 Work
Phase 5: Structure
During Phase 5, the concrete base, walls, column, beams, and roof elements of the UFES structure will be built, and mechanical and electrical equipment will be installed. The new electrical building will be installed as well. Concrete trucks and pumping equipment will be on site.
The City will continue to keep you informed of any exceedances of dust, noise, vibration, and groundwater levels, and corrective actions taken.
Phase 6: Site Finishing
Once the concrete structure is completed, the Event Center storage area will be repaved, with access hatches to components of the underground concrete structure. A new wall will be installed along Saratoga Drive, along with new plantings. 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 for Event Center usage.
The construction crews will be demobilized, and the new facility will undergo startup and testing. Neighboring properties participating in the ongoing condition assessments will receive their final, post-construction condition assessments.
The City will continue to keep you informed of any exceedances of dust and noise levels and corrective actions taken until earthwork ends.
Representation of Phase 6 Finished Site
How Will the Diversion Structure, Diversion Sewers, and Force Main Be Built?
To transport wastewater to the UFES, a diversion system, which includes a diversion structure, diversion sewers, and force main, is required along Delaware Street and Saratoga Avenue. To prevent SSOs, this diversion system will divert excess flows from the Delaware sewer trunk line, and convey the excess flows to the 5.3-million-gallon underground structure for temporary storage.
The diversion structure will be installed south of the intersection of Saratoga Avenue and Delaware Street. A new 36-inch diversion sewer will be installed using a combination of trenchless (horizontal directional drilling) and open trench construction methods along portions of Saratoga Avenue and Delaware Street. An 18-inch force main along portions of Saratoga Avenue and Delaware Street will be rehabilitated using a trenchless method to inject a lining into the existing pipe. If new pipe is needed for this force main, horizontal directional drilling methods will be used.
Traffic Management
Traffic control and management will be in place for the duration of the UFES and pipeline work. Construction traffic to and from the Event Center site is planned to be routed from Delaware Street through the access easement on the Event Center Property. Construction traffic from pipeline construction on Delaware Street and Saratoga Drive will be routed to the nearest designated and approved City truck haul routes: Delaware Street or Hillsdale Boulevard.
Dust Control
Dust control measures will be implemented throughout construction. This includes wet sweeping on surrounding streets and around the construction site, covering any truck beds hauling off dirt, site watering, tire washing facilities, and screening the site. A dust monitoring program will be implemented to ensure dust control measures are effective, and regular updates will be provided.
Future Operations and Maintenance
The UFES will be used during heavy storms, as well as for some collection system maintenance and inspection activities. It is expected to be used fewer than 20 times per year on average. During use, it will temporarily hold flows for up to 24 hours.
Dry Weather Conditions
During dry weather, the flow equalization system will rarely be used, except for maintenance and diversion, because the wastewater collection system has enough capacity.
Maintenance/Diversion
The equalization system will also provide temporary storage, or holding, to facilitate future sewer construction projects and operations and maintenance activities, such as pipeline inspection and cleaning.
During Heavy Rains
During storms, rainwater gets into the wastewater collection system and overwhelms its capacity. The excess, rain-diluted wastewater will be redirected to the temporary holding area to prevent overflows and to allow the system to better manage the large volumes of water in the system.
After Heavy Rains or Maintenance/Diversion
After the storm subsides, the diluted wastewater is released from the equalization system into the main wastewater collection system and sent to the treatment plant. When the system has been used for maintenance, the wastewater returned to the main collection system will not be diluted. Self-cleaning mechanisms are activated to flush and clean the equalization system, all while odor control is in effect.
Continuous Odor Control
After each use, the holding structure will be emptied and cleaned via large tipping buckets. Odor control facilities will be in continuous operation. The UFES will be inspected by the City after each use.
The CEQA Process
The Final Environmental Impact Report for this project is now available at the links below. Hard copies are also be available at City Hall and the San Mateo Main Library.
The Final EIR incorporates written responses to comments received during the public comment period, which ran from March 6, 2019 through May 31, 2019. The Final EIR will be presented to the Planning Commission and City Council for consideration of adoption.