Stanford model finds coordinated wastewater upgrades could cut Bay Area nitrogen costs

Stanford researchers estimate that three San Francisco Bay wastewater treatment plants could cut the projected cost of removing nitrogen by up to 48% if they coordinate upgrades. The September 24 study in Nature Water puts the largest modeled saving at $268 million over 30 years. That is a planning result, not money already saved or a measured reduction in household sewer bills.

The finding matters because Bay Area wastewater agencies face a requirement to reduce nitrogen discharged into the bay. Coordination could let plants choose where treatment is cheapest and delay some expensive construction. To turn that possibility into savings, utilities would have to agree on investments, satisfy their permit obligations and carry out the work.

Where the projected savings come from

The researchers built a decision-support tool called CLEANRWastewater to compare capital and operating choices over time for facilities sharing a regulated watershed. Their case study covers three treatment plants in the San Francisco Bay area. According to Stanford, the plants are within a few miles of one another, and the comparison spans 30 years of capital and operating costs.

In the model, coordinated decisions reduced the cost of nutrient removal in the shared subembayment by as much as 48%, or $268 million, compared with the study’s comparison scenario. The study attributes the savings to postponing capital-intensive upgrades and deploying the lowest-cost treatment options across the area, rather than planning each facility’s response in isolation.

The study’s framework can test uncertainty in future nutrient loads, a relevant question when planners must make decisions years before upgrades are complete. The accessible abstract does not provide all the cost assumptions, plant identities or detailed sensitivity results. Those limits make the headline percentage useful as a case-study estimate, rather than a promise that every Bay Area plant could achieve the same reduction.

The pollution rule behind the investment

The San Francisco Bay Regional Water Quality Control Board adopted a watershed permit in July 2024 requiring 40 sewage treatment plants to cut their collective nitrogen discharges by 40% from 2022 levels. The board linked the rule to a harmful algal bloom that year that triggered a major fish kill. It says excess nutrients can help fuel blooms that deplete oxygen in the water.

The permit gives agencies ten years to make improvements. The water board describes several possible approaches, from optimizing existing systems to installing new treatment processes. Wetlands and wastewater recycling are among the other options it identified. Board chair Alexis Strauss Hacker said the permit followed years of monitoring and research with wastewater agencies and the San Francisco Estuary Institute.

Those requirements create the setting for the Stanford model, but the study’s three-plant savings figure should not be applied to all 40 plants. Stanford separately estimates that independent upgrades across the wider Bay region could cost more than $10 billion and require roughly $200 in annual sewer-rate increases per household. Those are regional estimates, not the cost base from which the $268 million case-study saving was calculated.

What coordination would require

A shared plan would require more than identifying the cheapest treatment equipment. Utilities would need to decide how to divide investments and responsibilities while meeting enforceable discharge limits. Stanford reports that several Bay Area utilities were discussing regional coordination, but that most were waiting for an official regulatory framework before committing. Their current positions and any agreement among the three modeled plants have not been independently confirmed.

The water board has acknowledged that coordination can complicate schedules. Its Basin Plan amendment page says staff examined regulatory options for projects that may need more time because of interagency agreements, multiple permits or land acquisition. The page describes a narrow route to longer compliance schedules for certain projects; it does not establish approval of the arrangement modeled in the Stanford study.

One utility’s planning illustrates how many decisions remain even without a regional agreement. In a November 2025 board paper, Central Contra Costa Sanitary District described a planned full-scale demonstration of membrane aerated biofilm reactor technology for nitrogen removal. Staff said a pilot completed in 2024 showed promise, while full-scale testing was still needed to answer questions about performance, hydraulics, operations and maintenance. The paper does not establish the outcome of any later demonstration.

Central San’s paper said final limits would begin in October 2034 and that the district would need to comply by the 2035 dry season. That timetable puts pressure on agencies to choose and test treatment approaches before the deadline. It does not show that the district has joined the study’s proposed coordination strategy.

The gap between the model and rate bills

Stanford also reports an additional 32% modeled saving from beginning coordination now rather than waiting until 2045. That comparison shows how the timing of decisions affects the study’s scenarios; it is not a forecast of when utilities will reach an agreement. The research does not demonstrate actual regional savings, and no resulting household rate reduction has been documented.

The next practical questions are whether utilities can establish a joint plan, obtain a regulatory framework that accommodates it and verify that chosen treatment systems meet nitrogen limits. The model supplies an estimate of what coordination might be worth for three nearby facilities. The eventual cost to build and run upgrades, and any effect on rate bills, will depend on decisions and results beyond the published analysis.