Partially treated wastewater spills into Russian River after treatment plant power outage

An unknown volume of partly treated wastewater made its way into the Russian River between Guerneville and Monte Rio late last week during a winter storm that drenched Sonoma County and cut power to tens of thousands of residents across the region.

The spill involved what Sonoma County Water Agency officials estimated at less than 277,000 gallons of sewage treated to a secondary level at the Russian River County Sanitation District Treatment Plant at the end of Neeley Road, slightly upstream and across the river from the Northwood Golf Club.

It occurred late Friday night and early Saturday morning, after a power failure shut down the facility, Assistant Sonoma Water General Manager Pam Jeane said.

When power was restored, a programmable controller reset valves in the system, closing off access to the third treatment step and allowing flows to build up between the second and third treatment phases until the basin overflowed, Jeane said.

Sewage treated to a secondary level has had “large, inorganic material” removed, and “much of the organic material has been biologically neutralized,” Sonoma Water said in a news release.

“Secondary effluent has flowed through clarifiers to remove solids, but some suspended solids can remain that would be removed in the third, and final stage of the wastewater treatment process,” the agency said.

Some of the overflow stayed in the vicinity of the treatment facility, near or on land used to dispose of highly treated wastewater during the summer months. The remainder traveled through about a third of a mile of forest to the Russian River’s edge, Sonoma Water said.

But the land is so “wet and boggy,” Jeane said, that it’s impossible to determine how much effluent stayed on land or got into the river.

The river, dark and churning from recent rains, was flowing at a high rate at the time, exceeding 7,500 cubic feet per second, or more than 3.3 million gallons per minute, as measured at the Hacienda Bridge in Forestville.

Any spill would have diluted very rapidly, Jeane said.

“It’s still not OK,” she said. “It’s still not supposed to happen.”

Environmental specialists were dispatched to test for impacts to aquatic and terrestrial wildlife and found none, Sonoma Water said. Regulatory agencies, including the North Coast Regional Water Quality Control Board, California Department of Fish and Wildlife, National Marine Fisheries Service and the U.S. Army Corps of Engineers, also were notified, per protocol.

Waste water from the facility is normally treated to a high, tertiary level so it can be used, in part, to irrigate adjacent land and the nearby golf club during the dry summer months. Between Oct. 1 and May 14, the recycled water is discharged into the river at a rate of 1% of river flows.

The spill occurred during a storm that delivered more than 2 1/2 inches of rain to the Guerneville area between 8 a.m. Feb. 29 and midnight Saturday, the National Weather Service said.

Almost 38 inches of rain have fallen on the area since Oct. 1.

The district serves about 3,200 households in a 2,700-acre serve area along the lower river corridor between Rio Nido and Vacation Beach.

It is designed to handle 710,000 gallons a day during dry weather. The programming glitch that caused the valves to reset has been fixed, Jeane said.

You can reach Staff Writer Mary Callahan (she/her) at 707-521-5249 or mary.callahan@pressdemocrat.com. On X (Twitter) @MaryCallahanB.