Fire and Rain

California utility mitigates a disaster and minimizes system damage after wildfires.

Fire and Rain

Every municipality’s goal is ultimately to protect its residents — but losing 5 percent of your housing stock to wildfire can make that difficult. The resulting inflow to the wastewater system after such a catastrophe presents other challenges.

A wildfire burned through 36,800 acres of California’s Sonoma and Napa counties last October, and the city of Santa Rosa found itself picking up the pieces of 3,000 structures that had been obliterated.

While debris removal and other emergency services were still underway, the city’s water department had its own task — capping sewer laterals in an area at risk for system intrusion by remnants of the fire.

“The majority of the homes were completely destroyed — down to the foundations — and that left the sewer pipes exposed at the surface of the foundation, underneath the debris,” says Jillian Tilles, associate civil engineer with Santa Rosa and manager of the sewer capping project. “There was a lot of concern that the exposed pipe would be vulnerable to inflow and infiltration, allowing the debris and ash to enter into our system.”

When ash combines with water, it can calcify in a system, hardening into a blockage and potentially restricting or stopping flow. As a preventive measure against future system repair and line replacement, it was decided to cap sewer laterals. Two neighborhoods in particular in Santa Rosa were deemed high-risk due to topography and the fact that two lift stations servicing the area had been destroyed.

A contract for 88 obliterated homes in the Fountaingrove and Coffey Park neighborhoods opened up to bids in early February, and notice to proceed was issued later that month. Though the initial contract estimated a six-week project, it only took about three.

Tough terrain

“The topography and the damaged lift stations are the reason that the city chose to address this specific area. There were concerns about the debris causing overflows in the neighborhoods served by the destroyed lift stations,” Tilles says.

An area of mixed topography, the Fountaingrove and Coffey Park neighborhoods have many houses built into steep slopes, making them vulnerable to I&I. Because of the unusual terrain, the whole area is served by nine lift stations. Most of them sustained some damage in the wildfires, with two being completely destroyed.

Many laterals had already been capped during the initial debris removal, but the city still needed confirmation on each property in the predetermined zone.

“We would go onto the property and verify whether or not the sewer lateral was plugged by the contractors that did the debris removal,” Tilles says. “If we did not find proper evidence that it was capped, we located the sewer laterals to the best of our ability at the foundation in order to cap it at the foundation. If we were not able to locate it at the foundation, we capped it at the back of the sidewalk.”

Video was used to identify the open laterals, but workers ran into some issues.

“We anticipated being able to video a little bit more than we actually were able to,” Tilles says. “We were hoping to find a clean-out and run a video up to the foundation and identify a location at the foundation, but most of the clean-outs were one-way clean-outs, and we weren’t able to get any video equipment in there.”

As a result, many properties were capped at the sidewalk. If they had to dig up the sewer lateral at the property side of the sidewalk, they exposed it, installed a two-way clean-out, and brought the pipe up to within 2 feet of the surface.

“Our intention for bringing it up to the surface was so that as people begin to rebuild their homes, it was more accessible and easier to find,” says Lori Urbanek, deputy director of capital projects engineering for Santa Rosa.

Of the 88 homes listed in the contract, the city only ended up needing to cap 38 laterals after verifying that the other 50 had been capped during initial debris removal.



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