A spill of untreated wastewater occurred at the Russian River County Sanitation District treatment plant in Guerneville after heavy rainfall overwhelmed the system and the facility reached capacity.
The spill began at 7:14 a.m. on Tuesday, Jan. 6.
The spill stopped Thursday, Jan. 8, at approximately 6:50 a.m.
Heavy rainfall associated with an atmospheric river significantly increased flows into the wastewater system, creating a constellation of issues that led to a spill at the treatment plant. Sonoma Water will continue engaging the community as it works to better understand the causes of the incident and identify actions to help prevent similar events.
The estimated volume of the spill, which was composed of untreated wastewater and stormwater, was approximately 5,507,000 gallons.
The four million gallons figure represents a peak flow rate recorded at a single point-in-time, rather than a total volume discharged over the course of a full day.
During heavy storm events, flows to the plant can spike for short periods and then decrease as conditions change.
Heavy rainfall also caused stormwater and river water to enter the collection system through inflow and infiltration, which temporarily increased flows. More information about inflow and infiltration is available at www.sonomawater.org/pollutionprevention.
The spilled water traveled through a forested area before reaching the mainstem of the Russian River downstream of Guerneville.
River flows were elevated due to storm conditions, exceeding 30,000 cubic feet per second (just over 11 million gallons per minute) at the Hacienda Bridge.
No. During the spill response, the public was advised to avoid contact with river water downstream of the spill and at coastal beaches with posted advisories. All water quality advisories related to this incident were lifted Monday, Jan. 12, after sampling results met required standards.
Untreated wastewater can contain bacteria, viruses and other pathogens that may pose health risks, particularly to children, pets, older adults and people with weakened immune systems.
Sonoma County Department of Health Services advised people who came into contact with river water during the spill to shower, wash affected clothing and wash hands thoroughly. Pets were also advised to be rinsed off.
With precautions, yes. Sonoma County Public Health recommends wearing gloves, closed-toe shoes, long pants and long-sleeved shirts to protect against sharp objects, sun exposure and germs. People should also use sun protection, stay hydrated and bring a basic first-aid kit. Hands should be washed and showers taken after cleanup activities.
Drinking water systems are regulated separately. No impacts to drinking water systems were reported. Residents with questions were advised to contact their drinking water provider.
Drinking water systems are regulated separately. No impacts to drinking water systems were reported. Residents with questions were advised to contact their drinking water provider.
After the spill ended, staff reviewed flow data and storage volumes, conducted water quality sampling and completed cleanup and site inspections.
Wastewater treatment relies on beneficial bacteria that can be disrupted during heavy storm events. Microbes from the Sonoma Valley treatment plant were brought in to help reseed the biological treatment process following the high flows. Dry weather has allowed storm-event flows in the holding basins to be gradually returned to the plant for treatment. As the treatment process continues to recover, plant throughput can continue to increase.
Yes. Required notifications were made to regulatory agencies. Agencies notified included Cal OES, the North Coast Regional Water Quality Control Board, National Marine Fisheries Service California Coastal Office, Sonoma County Department of Health Services, the California Department of Fish and Wildlife Bay-Delta Region and the National Oceanic and Atmospheric Administration law enforcement division.
Information about the incident and response is available at www.sonomawater.org/rrcsd-spill.
Water quality test results can be found on the Sonoma County Environmental Health webpages for fresh and ocean water.