Thursday’s deluge caused sewage spills in four areas of Sonoma Valley as well as one location in Penngrove, Sonoma County Water Agency officials said.

Large amounts of untreated wastewater was overflowing from manholes onto various byways, including along Highway 12, at the intersection of Valletti and Cassabella drives, and on Fourth Street East at East Spain Street in Sonoma near Sebastiani Vineyards and Winery. In Penngrove, the sewage overflow was near the intersection of Ely Road and Old Redwood Highway.

“In Sonoma Valley, we have an older system with 50-plus-year-old pipes,” said Ann DuBay, a spokeswoman for the Water Agency. “So when a lot of water gets in there, it starts to overflow.”

DuBay said the problem was caused by Thursday’s heavy rains. Normally, about 4 million gallons of sewage and water is sent to the Sonoma Valley County Sanitation District, where it is treated. Runoff from the storm increased the flow to 14 million gallons, DuBay said. The district serves 17,000 households and businesses in the area.

Sonoma County officials are advising area residents to stay out of the stormwater, because of potential health and safety hazards.

“People shouldn’t be walking barefoot in the streets, or playing in the water,” DuBay said.

DuBay also said pets should be kept out of the flooded areas.

Water agency officials notified various health and regulatory agencies of the sewage spills.

You can reach Staff Writer Angela Hart at 526-8503 or angela.hart@pressdemocrat.com. On Twitter @ahartreports.