Benzene found in water outside Fountaingrove contamination area

Santa Rosa may be zeroing in on the cause of the contamination in the water supply of the devastated Fountaingrove neighborhood, but there are also troubling signs that the problem may extend beyond the immediate advisory area.

Since Jan. 24, when the city last released detailed test results, the city has found 58 additional instances of benzene in the drinking water in the Fountaingrove area. The vast majority came from the 184-acre area north and south of Fountain Ggrove Parkway around Fir Ridge Drive, an area once home to 350 families. Only 13 homes remain following the October wildfires.

Residents of the area have been under a strict advisory for months to not drink or boil the water while the city tries to find the source of the contamination and fix the problem, something that could cost upwards of $20 million if the area’s water system needs replacement.

But a handful of tests have recently detected benzene in areas outside the advisory zone, a new development that may complicate the 3-month-long hunt for the cause of the contamination.

In response, the city is launching a more aggressive regimen of water tests covering all the burned areas of the city, including Coffey Park, in its effort to make sure other burn zones aren’t experiencing similar problems.

“We just don’t want to leave any stone unturned going forward,” Ben Horenstein, the director of Santa Rosa Water said Thursday.

The new sample results are out of 242 tests the city has conducted since Jan. 24. That means about a quarter of the samples the city is taking are showing benzene, a chemical commonly found in plastics and gasoline that is a human carcinogen.

That latest results bring to 145 the total number of tests confirming benzene at levels that exceed state standards. The maximum containment level (or MLC) for benzene in drinking water in the state is 1 part per billion.

The newest results are similar in range to those that have had been discovered before Jan. 24, with some exceptions.

The first batch contained four test results showing benzene levels over 500 parts per billion, one of which was as high as 918 parts per billion.

This time, however, there were no results over 500 parts per billion. There were three3 between 10 and 500 ppb, 10 between 25 and 100, 16 between 5 and 25 ppb, and 29 between 1 and 5 ppb.

But seven of those results were from outside the existing advisory area. Six of those results were under 10 ppb, while the seventh was something of an outlier at 240 parts per billion, Horenstein said.

Before last week, the city had only received one positive test for benzene outside the advisory area, and it disappeared and didn’t return after some equipment was replaced.

The city is now replacing the high-density polyethylene service lines that lead to those seven locations, and plans to test them to see if it fixes the problem, said Jennifer Burke, the city’s deputy director of water and engineering resources.

All the seven locations are located at burned home sites. No tests performed at existing homes have shown contamination since the area was isolated, Burke said.

A forensic chemist helping the city analyze the results has helped the city rule out one possible source.

None of the samples have shown any isooctane, suggesting the contamination source is not from a petroleum product like gasoline, Horenstein said. It was possible that an underground storage tank was responsible, but this allows the city to rule that out, Horenstein said. The presence of vinyl chloride in some of the samples, however, suggests the high-density polyethylene service lines or other plastic components in the system are the most likely culprit at this point, Burke said.

Such results indicate “constituents that are evidence of combustion or melting plastic of some sort,” Burke said.

The increasing confidence that components in the city’s own water delivery system may have been compromised by the fire in way that is contaminating the water is driving the more aggressive testing plan, Horenstein said.

Instead of merely testing at sampling stations, which draw the water from the mains, suspicion that the plastic laterals or other components are responsible necessitates more exhaustive testing of laterals in other areas, as well, he said.

The city has been in contact with state regulators and is not expanding the advisory area at the moment, Horenstein said.

That’s because the location of the results from seven spots outside the advisory appear isolated, he said.

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