Santa Rosa wastewater plant releases treated sewage following deluge

Overwhelmed by record rainfall this week, Santa Rosa’s regional wastewater treatment plant has released about 22 million gallons of treated sewage into two creeks and the Laguna de Santa Rosa since Wednesday, and the discharge will continue indefinitely with another storm on the way, officials said Friday.

All three waterways drain into the Russian River.

It was further evidence that the deluge, which swamped Russian River communities and displaced thousands of residents this week, had far-reaching impact.

The releases began Wednesday, a day after Santa Rosa received 5.66 inches of rain, a record for one-day precipitation dating back to 1902.

It took about a day for the added volume of sewage mixed with runoff to reach the plant on Llano Road, which treats wastewater from about 230,000 customers in Santa Rosa, Sebastopol, Cotati and Rohnert Park.

The record-breaking rain from an atmospheric river that stalled over Sonoma County “put a total strain on the system,” said Emma Walton, interim director of Santa Rosa Water.

Santa Rosa’s was at least the second municipal treatment plant overwhelmed or knocked out by this week’s storm. Healdsburg earlier this week declared an emergency stemming from problems at its own flooded facility.

Rainwater seeping into Santa Rosa’s far-flung sewage collection system boosted the flow arriving at the plant to as much as 105 million gallons a day this week, the largest flow ever recorded.

Normal wintertime inflow is ?19 million gallons per day, city spokeswoman Adriane Mertens said.

On Friday, the inflow was 48 million gallons a day.

The sewage surge prompted plant operators to discharge fully treated sewage from two storage ponds: one on Llano Road across from the plant, the other on Willowside Road. The water went into Colgan and Santa Rosa creeks and the Laguna de Santa Rosa, which flows past the treatment plant.

The inflow also filled emergency holding basins designed to store raw sewage upstream from the plant, forcing operators to push sewage through the plant too fast to complete the final stage of treatment. The under-treated sewage was sent to the three isolated storage ponds, Walton said.

At no time was untreated or partially treated sewage released into the environment, she said.

No plant facilities were overrun by floodwaters, which are themselves a hazard to public health.

“Floodwaters may contain a variety of hazards including submerged debris, contaminants, agricultural wastes and runoff and other unknown hazards. People should use an abundance of caution around floodwaters,” Sonoma County Health Officer Dr. Karen Holbrook said.

As a result of flooding around the plant on Wednesday, a Santa Rosa Fire Department swift water rescue team ferried sewage plant operators out to one of the ponds to conduct the discharge, Mertens said.

The flood conditions also prevented operators from monitoring the discharge to the degree required by the city’s operating permit, Walton said.

City officials must submit a report on that shortcoming to the North Coast Regional Water Quality Control Board within five working days and have been in touch with the agency this week, she said.

Meanwhile, the city is monitoring weather reports on an atmospheric river expected next week to determine how it manages the system, Walton said.

Santa Rosa operates the system with a “zero discharge” goal, she said, recycling as much treated sewage as possible. The last such discharge was in 2017.

In Healdsburg, floodwaters poured into two buildings at the city’s wastewater plant, including the operations headquarters, damaging motors at the facility and halting treatment. Damage to the plant had been estimated at hundreds of thousands of dollars, officials said.

On Friday, the city said it had restored operations at the plant.

But officials also expressed concern Friday that about 1 million gallons of sewage stored in ponds had seeped through the soil to the Basalt Pond, a gravel pit excavated in the floodplain of the Russian River, and may have impacted the river.

The city said it is working with the regional water board to resolve the matter.

A Sonoma Water spokeswoman could not be reached Friday for information about operations at the Sonoma Valley sewage treatment plant, which often reports discharges of untreated wastewater during periods of abundant rainfall.

Staff Writer Kevin Fixler contributed to this report. You can reach Staff Writer Guy Kovner at 707-521-5457 or guy.kovner@pressdemocrat.com. On Twitter @guykovner.