Santa Rosa: Fountaingrove water system needs $43M replacement after Sonoma County wildfires

The entire water-delivery system in a 184-acre section of the devastated Fountaingrove neighborhood will likely need replacement after becoming contaminated with benzene, and it appears the city will initially be on the hook for a project whose estimated costs have soared to $43 million.

The intensive investigation into the exact cause of the contamination continues, but officials say they now understand how the cancer-causing hydrocarbon found in gasoline and plastics made it into the water mains in the area.

The city’s team of water engineers, consultants and regulators is “converging on the recommended approach” that would require the “full replacement of the distribution system, from the water mains to the meters on the properties” and related equipment like fire hydrants within the advisory area, Ben Horenstein, director of Santa Rosa Water, said Thursday.

The cost of that solution, which Horenstein had previously estimated at up to $20 million, has now more than doubled, and completion may take significantly longer than the year he initially hoped.

The development raises a host of questions about how quickly the devastated Fountaingrove neighborhood, which lost 1,420 homes in the Tubbs fire, may be able to recover, how the city can fund the needed repairs, and what it means for residents who still live there.

Before the fire, there were 350 homes in the advisory area, centered on the north and south sides of Fountaingrove Parkway near Fir Ridge Drive. Restrictions on water use for the 13 homes that remain standing have been in place since November. While lots are being cleared, few former residents of the advisory area have applied for city permits to rebuild.

Contamination of the water system has become one of the most pressing and confounding challenges facing the city as it seeks to recover from the October wildfires, the most destructive in U.S. history, with 5,100 homes lost in Sonoma County alone. Melted plastic storm drains that caused sinkholes and confusion over the acceptable level of arsenic in soil before cleared lots could be rebuilt have also been curveballs, but nothing like the contamination problem.

City officials say it has become increasingly clear over recent weeks that the benzene and other hydrocarbons detected in the water system in the advisory area originated when plastic components of the system melted during the fires and were somehow sucked into the water mains though a severe drop in water pressure.

Normally, positive water pressure pushes contaminants outward, acting as a protective barrier against broader contamination of the system, Horenstein said.

In this case, however, the sharp drop in water pressure that the Fountaingrove area suffered during the fires — something firefighters complained about as they battled the blaze — likely created a vacuum effect on the system.

Water pressure in the hillside neighborhood is provided by a combination of pumps that send the water uphill and pressure from the millions of gallons capable of being stored in seven holding tanks in the area.

But at the time of the fire, one of those tanks was empty because it was down for seismic retrofitting, said Jennifer Burke, the city’s deputy director of water and engineering resources.

It’s not clear how much having that tank offline contributed to the low water pressure, but it likely had some impact, Horenstein said. It also wasn’t immediately clear how full the other tanks were at the time of the fire.