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Stormwater runoff overwhelms San Luis Obispo’s aging sewer system


More than fifteen thousand gallons of sewage spilled into San Luis Obispo creeks and streets this week. County public health officials say the two spills—one via a manhole cover on Broad Street downtown and another from a mainline into Acacia creek—were stopped and cleaned up, but advise the public to avoid Old Garden and Acacia creeks over the next three days.  

The city of San Luis Obispo’s wastewater division said the spills were the result of stormwaters overwhelming an aging sewer system.

David Hix is with San Luis Obispo’s wastewater division.

"We have seven people dedicated to our wastewater collection, and we do inspections almost daily," Hix said. "We have a video camera that videos it. We have also done studies to help us understand where we experience inflow and infiltration the most."

Inflow and infiltration, or I&I for short, is when stormwater runoff goes down the city's drains and overflows underground pipes.

"Our system is fairly old, we have pieces of pipe in our system that are over a hundred years old," Hix said.

Even some of the newer pipes are made of clay and cast iron, Hix said, and as part of the capital improvement plan, each year the city replaces some of the sewer infrastructure with higher density plastic pipes.

But that doesn’t account for the pipes of homes and business, called sewer laterals.

"We have about as many miles of sewer laterals as we do public sewer main," Hix said. "And we don’t own those. So part of this is determining how serious the problem is with sewer laterals, and we think it’s a significant contribution to I&I." 

Homeowners are responsible for the maintenance of their sewer pipes, extending to the city mainline. Hix said in April, the wastewater division plans to talk to the San Luis Obispo City Council about offering home and business owners financial assistance to help them replace or upgrade their pipes.