Collaborating Across Agencies to Deliver Sustainable Nutrient Strategies  

Elevated nutrient concentrations in aquatic systems can result in elevated algae growth, oxygen depletion, and harmful by-products that can damage wildlife and ecosystems. Historically, San Francisco Bay has been resilient to such algal blooms despite significant nutrient inputs. This resiliency is attributed to a combination of high turbid waters, strong mixing, and filter-feeding clams. A significant harmful algal bloom in 2022 signaled a shift in the Bay's resiliency against such high nutrient levels. To protect beneficial uses, regulators imposed Baywide nitrogen load limits in 2024 that need to be met by May 2035.

One promising approach to regional nitrogen management from wastewater dischargers is the implementation of nature-based solutions (NbS), such as open-water treatment wetlands and horizontal levees. 

Since the inception of the Nutrient Management Strategy group for the Bay Area Water Resource Recovery Facilities (WRRF) in the mid-2000s, HDR has supported and engaged in its evolution, from viewing nutrients as a WRRF discharge-specific issue to the development of WRRF-led multi-benefit regional solutions, including NbS. Such natural systems represent an alternative or complement to mechanical technologies.  

In 2019, a collaboration between the San Francisco Estuary Institute (SFEI) and the Bay Area Clean Water Agencies led to the identification of opportunities for wastewater agencies to reduce nutrient loads discharged to the Bay by implementing multibenefit NbS.  

In a multiphased approach, SFEI used a GIS suitability model to identify potential locations for NbS at the 37 treatment plants discharging to San Francisco Bay. In the second phase, SFEI collaborated with staff at eight facilities to develop preliminary NbS concepts. In the final stage, the SFEI coordinated with HDR to develop draft reports outlining early concept designs and cost estimates for three sites: Delta Diablo, Fairfield-Suisun Sewer District, and San Jose-Santa Clara Regional Wastewater Facility.

The next steps for implementation involve determining project goals and objectives, selecting preferred designs, refining cost estimates, and initiating early conversations with permitting agencies and community input. Effective nutrient removal requires ongoing coordination with multiple partners before advancing further in the design development process.