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Introduction

Coyote Point Park and its distinctive grove of eucalyptus trees stretch along one of San Francisco Bay’s southern peninsulas. It is a picturesque scene typical of northern California and the City of San Mateo. The municipal pump station located nearby is a recently commenced, five-year multi-phase renovation project, as the county looks to repair or replace 11 pump stations in the surrounding area. The initial work took place along the coast just west of the 670-acre park, but the first phase was met with stormwater challenges, potentially jeopardizing the newly renovated project.

Goals

The priority was to acquire a high-flow trash capture system to help the City of San Mateo meet their Long-Term Trash Load Reduction Plan, while prolonging the longevity of the pump station that conveys stormwater flows safely into the San Francisco Bay. The system needs to address the removal of total suspended solids (TSS) and meet the requirements of California full capture to properly detain sediments and trash within stormwater runoff before reaching the pump station.
Site constraints were identified early in the project, guiding the renovation design process. A high groundwater table due to proximity to the bay requires extensive dewatering for any deep underground installation, so a shallow-profile system was preferred. Secondly, the Coyote Point site was hindered by low-hanging powerlines, limiting the use of cranes. This obstacle limited installation and design options, therefore the specified stormwater treatment device would need greater flexibility, and the capability of on-site concrete vault construction and internals installation.
Lastly, the long-term device maintenance plan was of utmost importance to the City, preventing costly damage to the pump system and the beneficial use of the San Francisco Bay.

Solution

With difficult site constraints in mind, the civil engineering firm Schaaf and Wheeler contacted Bio Clean for a solution. This collaboration lead to the implementation of the DSBB Separator. This hydrodynamic separator is a shallow-profile, full capture treatment device that is easily adaptable to cast-in-place field installation, making it the top choice for the Coyote Point site.
With BMP sizing criteria for the Coyote Point site performed by Schaaf and Wheeler, Bio Clean designed an 11 x 34 foot DSBB Separator to fit the parameters. This large DSBB would meet their pollutant removal goals, as it is proven to remove 80% TSS and capture 100% of trash 5mm and larger, properly protecting the renovated pumps from plastics, trash, and other damaging pollutants.
The design of the DSBB allows the newly improved internals to be assembled inside the cast-in-place vault at the job site, eliminating the use of a crane and safely avoiding low-hanging power lines.

Conclusion

Proximity to San Francisco Bay introduced a list of challenges for the project and required the engineers to address system sizing and installation methods without compromising performance. The 11 x 34 foot DSBB is the treatment device that the city and county needed to handle full trash capture in high-flows while reducing maintenance, and providing protection to the newly renovated pumps.

REFERENCES
1 https://en.wikipedia.org/wiki/Coyote_Point_Recreation_Area
2 https://www.cityofsanmateo.org/3397/LitterTrash-Reduction

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