Burned storm drains in Santa Rosa create slide, sinkhole risk

by Michael Mosher on November 28, 2017

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Santa Rosa officials warned Sunday of a new threat posed by last month’s devastating wildfires — sinkholes and landslides.

Extreme heat from the blazes that destroyed more than 5,000 homes and killed 23 people also melted plastic storm drains underground, creating the risk of collapse or slides with the upcoming rains.

Officials identified eight areas, all in the Fountaingrove area, where high-density polyurethane pipe had been damaged and 20 other areas where the pipe was suspected of being compromised.

None of the pipes, which were both publicly and privately owned, appeared to run beneath homes but at least one crossed under a road. The cost of the damage, discovered Thursday, was not released.

Deputy Fire Chief Bill Shubin said residents should be alert as storms sweep in Monday morning and continue on and off through the week. Officials have gone door to door in affected neighborhoods, hanging fliers with information about the damage and advice on precautions to take.

“I want to emphasize it’s a fluid situation,” Shubin said at a press conference Sunday at the Finley Community Center. “We know the rain is coming and we want to be prepared.”

He said up to a “couple of hundred” residents in isolated geographical areas could be at risk. Teams of engineers and geologists fanned out to assess remaining pipes using closed-circuit TV cameras.

“Residents should be prepared to leave,” Shubin said.

The only sinkhole to open so far was on sloping land between undamaged homes off Newbury Court. Fire apparently ignited the exposed end of the 24-inch diameter pipe and continued burning underground about 250 feet. The ground gave way, leaving a 7-foot deep by 4-foot wide trench. By Sunday, crews had excavated the old pipe and laid a new one.

At another potential site, a 15-inch pipe had burned away under Cross Creek Road between Silver Fox Court and Bridlewood Court. That portion of Cross Creek Road was being closed Sunday afternoon so the drain could be repaired, said Paul Lowenthal, the city’s assistant fire marshal.

Officials said the Fountaingrove was especially prone to the problem because it is newer than other neighborhoods, where concrete and steel pipe was common.

Heaven Moore, the city’s supervising engineer for storm water drains and creeks, said the plastic piping came into use about two decades ago. City codes require the last 20 feet to be constructed of corrugated metal material, in part to avoid fire risk, she said.

It was too soon to say if pipes were installed incorrectly and who was to blame, she said.

During the coming rains, the city will have crews in the field to watch for flooding, slides and sinkholes and to assist with public safety, said Bennett Horenstein, the city’s water director. The county will also reopen its emergency operations center, he said.

Santa Rosa Mayor Chris Coursey said the storm drain problem is the latest in a series of setbacks that continue to unfold in the wake of the fires.

“What I’ve learned over the past four or five weeks is this disaster has layers of complexity,” Coursey said. “You’d think pipes underground would be safe. They’re not. Again, we’re finding out things every day that we didn’t know before.”



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