Heavy rains cause sewer overflows

Heavy rainfall has caused nine wastewater overflows in Sonoma Valley, including at the Sonoma Charter School and Flowery Elementary School campus. A majority of what the Sanitation District calls “sanitary sewer overflows”  occurred in the Boyes Hot Springs and Fetters Hot Springs areas, with two overflows in Eldridge.

Nearly 2 inches of rain was measured during a 24-hour period ending Tuesday at 9 a.m. at the Sonoma Valley wastewater treatment plant. Other areas of the valley reported 3 inches of rain overnight.

During heavy rain events the District’s wastewater collection system can become overloaded due to inflow and infiltration of rainwater and groundwater into sewer mains.

Wastewater maintenance and work crews, including biologists, responded to the separate waste overflows starting at 2:30 a.m. Tuesday. Officials said that Sanitation District staff are working to minimize the flows as much as possible, evaluate any impacts to public and environmental health, and will continue to monitor the collection systems. The State Office of Emergency Services and California Department of Fish & Wildlife have been notified.

The Sonoma Valley wastewater treatment plant is capable of treating up to 12 million gallons per day (mgd) and storing up to 35 million gallons of untreated wastewater, but during heavy rain events inflow into the plant can more than triple. Prior to the storm on Monday and early Tuesday, inflow to the treatment plant was about 4 mgd. During the peak of the storm the plant was taking in between 16 and 17 mgd.

The wastewater collection system treats wastewater from approximately 17,000 equivalent single-family dwellings within the City of Sonoma and the unincorporated areas of Agua Caliente, Boyes Hot Springs, Eldridge, Fetters Hot Springs, Glen Ellen, Schellville, Temelec, and Vineburg.

Another contributing factor to the overflow events, which the District said it is addressing, is leaky private sewer laterals and illegal connections of roof downspouts, yard drains, sump pumps and other non-sewer discharges into the sewer system that can greatly increase the amount of wastewater entering the system during storms.

A new ordinance requires that older lateral pipelines be inspected and repaired, if necessary. Find out more about wastewater treatment by checking out Cleanawater

Letter: Water overflow poses disease threat