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water quality

Napa County wildfires bring water quality challenges

Milliken Reservoir

Burned wildlands from the Atlas Fire surround the Milliken Reservoir, one of the city of Napa’s two local reservoirs. Burned away vegetation can lead to erosion, hurting water quality.

Napa County’s recent spate of wildfires is that rare case when fire can hurt water.

Communities must deal with potentially water-fouling ash and erosion in coming months. The city of Napa, Calistoga, Yountville and the Veterans Home of California at Yountville all saw fires burn up to the shores of their reservoirs.

Though none of the communities is without drinking water, the situation could at the very least pose water treatment challenges as the rainy season kicks in, officials said.

“It’s always a concern when you have a fire in a runoff area,” Calistoga Public Works Director Mike Kirn said Wednesday.

Napa County recently found out why. The 2015 Valley Fire in Lake County burned in the Putah Creek watershed, leading to trouble for water systems serving the small, rural communities of Berryessa Estates and Berryessa Highlands.

The problem didn’t appear until this past winter, about a year and a half after the blaze. Unusually big storms finally carried the ash down from the watershed into Putah Creek and ultimately into Lake Berryessa.

“Once it came, it was goo,” said Phillip Miller, engineer for the two water systems. “Ash is a very, very fine material.”

As a result, the water treatment plants for the Estates and the Highlands closed down for a couple of weeks. The two communities had enough water in storage tanks to tide them over.

“It eventually does settle,” Miller said. “Once we got water clear enough to treat, we went back online.”

Whether the Estates and Highlands experience has any relevance for Milliken, Rector and Kimball reservoirs remains to be seen.

“Every one is a unique circumstance,” Miller said.

The city of Napa’s Milliken Reservoir is dirtier in the wake of the Atlas Fire, though Napans will have enough clean water to slake their thirst in coming months. City Water General Manager Joy Eldredge said Milliken usually provides the city’s highest-quality water.

Nestled in the mountains east of Napa, the reservoir was in the path of the blaze. The watershed is charred and burned, making it prone to erosion with the winter rains. Ash fell into the water.

Ash is an enemy for water quality.

“It’s organic carbon,” Eldredge said. “Those are the things we try to remove through our treatment process.”

Napa typically doesn’t use Milliken Reservoir during the winter and has already stopped using it this year because of the Atlas Fire. The fire compromised the above-ground pipe that feeds the water treatment plant by burning some of the wooden supports.

Eldredge said the city will see next year if the reservoir has higher organics. By then, the small reservoir should have spilled with the winter rains.

Even in a worst-case scenario – Milliken Reservoir can’t be used for some time – Napa should have enough water next summer because Milliken isn’t the city’s prime water source.

Milliken Reservoir can store 1,390 acre-feet of water, compared to 31,000 acre-feet for the city’s Lake Hennessey reservoir. Lake Hennessey is located in the mountains east of Rutherford away from the burned areas.

In addition, Napa has rights to 21,900 acre-feet of water annually from the State Water Project that makes use of Sierra Nevada snow melt, though the actual allocation in a typical year is 13,500 acre-feet. An acre-foot is about 326,000 gallons.

“That’s the beauty of our three different supplies and reliability,” Eldredge said.

Still, she said, it’s good to have high-quality Milliken water in the system during high-use times in the summer. Among other things, the supply helps with system water pressure.

The Atlas Fire could have wreaked worse havoc on Napa’s Milliken Reservoir system. Somehow, the fire missed burning treatment filters that are worth more than a million dollars apiece.

“It jumped right over them….We’re happy to see they still exist,” Eldredge said.

The city of Calistoga’s webpage said that Kimball Reservoir during the 1950s held 345 acre-feet of water. That amount has since shrunk to 312 acre-feet because of sediment that washed into the reservoir. The city blames a 1985 fire that burned the watershed, leading to erosion.

Now the city must deal with the Tubbs Fire aftermath. Burn maps on the county webpage show the fire burned up to the northern shore of the reservoir.

“It’s pretty much the whole St. Helena mountain that has been burned up,” Kirn said. “That’s our watershed.”

Calistoga is evaluating the possible impacts and could seek outside help on such efforts as hydroseeding the watershed to prevent erosion, he said. Perhaps light rains predicted for Thursday will start vegetation sprouting.

But the Tubbs Fire didn’t force Calistoga to stop using Kimball Reservoir water.

“Our plant was in continuous operation through the whole event,” Kirn said. “We didn’t skip a beat.”

June Iljana of the state Department of Veterans Affairs provided an email update from agency water officials on the Rector Reservoir. The reservoir is run by the agency and serves both the Veterans Home of California at Yountville and Yountville.

Rector Reservoir also continued providing water during the Atlas Fire, even though the fire burned close to the water’s edge. Testing showed the turbidity and pH are similar to levels before the fire.

Rains will likely wash ash into the water, resulting turbidity and pH level increases. Water treatment plant staff will make the necessary adjustments, the email said.

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Napa County Reporter

Barry Eberling covers Napa County government, transportation, the environment and general assignments. He has worked for the Napa Valley Register since fall 2014 and previously worked 27 years for the Daily Republic of Fairfield.

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