Supporting Bay Area Nutrient Optimization

The iconic San Francisco Bay is one of the world’s greatest natural resources. As the largest estuary on the Pacific coast, its value to the California economy is enormous, and its biodiversity significantly contributes to the quality of life for nearly 7 million Bay Area residents.

While nutrient discharges to the Bay have not created impairment problems (e.g., excessive algal growth), recent studies have shown that its historic resilience to nutrient loading may be weakening. As a result, nutrients are a growing concern for the health of the ecosystem.

It is estimated that 63% of the annual average total nitrogen load to the Bay is from publicly owned treatment works. In response to this, the Regional Water Quality Control Board expressed the intention to require POTWs to meet more stringent regulations in the future.

The Regional Board adopted a Nutrient Watershed Permit in April 2014 that requires all municipal Bay dischargers to conduct studies for the optimization and upgrade of their facilities. The Bay Area Clean Water Agency (BACWA) is coordinating these studies for its 39 member POTWs.

For the First Nutrient Watershed Permit, HDR provided a nutrient reduction study that evaluated opportunities for nutrient treatment via optimization, upgrades and sidestream treatment, and prepared group annual reports.

For the Second Nutrient Watershed Permit, our team prepared group annual reports (2019-2024) and provided as-needed services. We coordinated with discharger agencies to collect the previous year’s nutrient loading data, reviewed and compiled the data, coordinated with the discharger agency to resolve data gaps and inconsistencies, prepared a draft appendix for each discharger agency for their review and comment, and then compiled their agreed-upon data and results into the main report. Following submission of the final report (each year), we supported BACWA with the preparation and presentation of materials at the annual retreat at Pardee and subsequently presented the information to BACWA’s membership at the annual meeting.

For the Third Nutrient Watershed Permit, we are continuing our collaboration with stakeholders to collect and monitor Compliance Milestone Reports. These reports inform the Regional Water Quality Control Board of progress on nutrient management projects across the Bay. We are preparing group annual reports, milestone updates, and a regional plan that will summarize progress for the 2026 and 2027 reporting years, through March 2029. The Watershed Permit outlines requirements for an aggregate dry season total inorganic nitrogen (TIN) load reduction of 40%, along with a 10-year compliance schedule to achieve these reductions. 

HDR also assisted with writing a portion of the scoping and evaluation plan as described under the second permit. In addition, we prepared nutrient reduction study reports for 37 BACWA member agencies to evaluate potential nutrient discharge reduction strategies and costs for treatment optimization, sidestream treatment, treatment upgrades, or nutrient load reduction by other means (e.g., recycled water for irrigation).