Petaluma's sewer plant gets a new five-year permit for winter discharges to the river

By The Downspout · Posted Oct 22, 2026 · 5 min read

Petaluma's Ellis Creek sewer plant can put treated wastewater into the Petaluma River from October 21 to April 30. On October 14, 2026, the San Francisco Bay Regional Water Board adopted a new five-year permit that sets limits on what that water can contain. It takes effect December 1, 2026.

Where it is and what it does

The Ellis Creek Water Recycling Facility is the City of Petaluma's sewer treatment plant. It is at 3890 Cypress Drive, Petaluma, ZIP 94954. See it on a map: Ellis Creek Water Recycling Facility, Petaluma.

It cleans the wastewater from sinks, toilets, businesses and industry. It serves the City of Petaluma and nearby unincorporated parts of Sonoma County, about 63,000 people.

The plant cleans the water in several steps: screens, treatment basins, ponds, wetlands and chlorine. The part of the water sent out for recycling also gets extra filtering and ultraviolet light.

In the dry season, May 1 through October 20, the plant does not release water to the river. It sends it to pastures, vineyards, golf courses, schools and other landscaping. Over the last four years, the plant recycled about 700 million gallons a year, about 30 percent of its wastewater, on more than 1,000 acres. Our page on where wastewater goes in Sonoma County explains the wider picture.

In wet weather, when those fields are soaked, the plant releases treated water into the Petaluma River through one outfall pipe. That is the pipe that carries the water out to the river.

What happened

On October 14, 2026, the San Francisco Bay Regional Water Board adopted a new permit for the plant. This is the regional state water quality board for the San Francisco Bay region, which includes Petaluma. Below, we call it the Regional Water Board. The permit's number is Order R2-2026-0021.

The permit is written under the federal Clean Water Act. Its formal name is a National Pollutant Discharge Elimination System permit, or NPDES permit. It is the legal permission for a plant to put treated water into a river, and it sets the limits.

Board staff expected no one to object. The permit takes effect on December 1, 2026 and expires on November 30, 2031. On December 1, it replaces the plant's earlier permit.

The plant can release water to the river only from October 21 to April 30. The permit bans releases from May 1 through October 20. The only exception is when the treated flow is more than the recycling pipes and storage can handle, and not because the City failed to supply recycled water. Then the City of Petaluma must explain why in its next monitoring report.

Each limit below is a cap on what the treated water can contain.

Solids and organic waste: the monthly average cannot be above 30 milligrams per liter. The plant must also remove at least 85 percent of them.
Ammonia: the monthly average cannot be above 3.0 milligrams per liter.
Copper: the monthly average cannot be above 7.0 micrograms per liter.
Bacteria: the plant tests for a germ called enterococcus. The average over six weeks cannot be above 30 per 100 milliliters. Also, no more than 10 percent of samples in a month can be above 110 per 100 milliliters. The earlier permit's bacteria limit was a monthly average of 35 per 100 milliliters.
Harm to aquatic life: the water is tested on small living test organisms, using a mix of 31 percent treated water. No single test may fail on a measure of harm short of death. In any month, no more than one failed result of any kind is allowed.

Within 180 days of the permit taking effect, the City must also send the Regional Water Board a report on any changes to its limits on what industrial users can send to the sewer, with a plan and schedule.

Two other permits set requirements for mercury, PCBs and nutrients. This permit does not change them.

The regional water plan bans discharges that do not get at least 10-to-1 initial dilution, and discharges into shallow water. The Regional Water Board made an exception here. It found no practical alternative in wet weather. The order says moving the outfall would need a pipeline about 100,000 feet long.

As a condition, the treated water must sit in the ponds or wetlands for at least one week first. The City's modeling found the water reaches a 3.25-to-1 mix within about 56 acres. The Regional Water Board calls that about 1 percent of the river in the most cautious case.

What it means for you

If you live in Petaluma or use the river, winter is when treated water goes in. The permit window for that is October 21 to April 30.

If you have a question about the permit, call Jerry Xu, a water resource control engineer at the Regional Water Board, at (510) 622-2469.
For the permit's supporting documents and the comments received, call the Regional Water Board's custodian of records at (510) 622-2300.
The order lists the plant's operations supervisor as its facility contact: (707) 776-3777.
If you disagree, the order says any person harmed by the decision can petition the State Water Resources Control Board. The petition must be received within 30 calendar days of October 14, which is November 13, 2026. The hearing notice says a petition can raise only issues that were raised at the hearing or in comments filed on time. For advice on your own case, ask a lawyer.

Our view: we favor healthy rivers and creeks, so the dry-season ban is the part we would point to. The ban helps reduce the plant's contribution to the river's nutrient problem. The order lists the tidal part of the Petaluma River as impaired by diazinon, nickel, nutrients and pathogens (disease-causing germs). Impaired means it is on a federal list of waters expected not to meet water quality standards.

What happens next

The permit takes effect on December 1, 2026 and runs through November 30, 2031. The City must apply to renew the permit by March 1, 2031.

Where this came from

The Regional Water Board's final order and its fact sheet, adopted October 14, 2026. The board's staff report and meeting agenda for the same day. The hearing notice for the draft permit. And the state's notice about the permit, posted October 19, 2026. All are listed below.

Sources

Checked 2026-10-22. Rules and programs change. If something here is out of date, the source above wins. Spot an error? See our corrections policy.