Sierra Water-Pure No More

Rim Fire pushes deeper into Yosemite, threatens Bay Area water source - San Jose Mercury News

The largest wildfire in the United States continued its destructive march through the Sierra Nevada on Tuesday, pushing further into Yosemite National Park and for the first time burning nearly to the edge of Hetch Hetchy Reservoir, the linchpin of the water supply for 2.6 million Bay Area residents from San Francisco to Silicon Valley.

via Rim Fire pushes deeper into Yosemite, threatens Bay Area water source – San Jose Mercury News.

The fire has burned up almost to the lake, and ash is accumulating on the surface.  But the intake pipe for San Francisco’s water is 260 ft below the surface.  It could take a while for the ash to filter down that far.

In a race against the fire, the agency has increased water releases from Hetch Hetchy to the maximum rate possible– 302 million gallons a day. The water flows down 160 miles of gravity-fed pipes and tunnels to the Bay Area, where it is stored in Bay Area reservoirs like Crystal Springs in San Mateo County and San Antonio in Alameda County.

Because the water comes mainly from snowmelt in the Sierras, it is only treated with chloramine and ultra-violet light, but  is not filtered.  Depending on the amount of ash and the runoff from burned areas, that could change.  San Francisco does have some filtering capabilities, but is it enough for all the water they use?

Meanwhile, the fire continues to spread east  into Yosemite.

By Tuesday it had burned 41,000 acres inside the park, nearly twice as much as the day before. Most of the charred area is in the remote, northwestern corner of the park.

Much of the park remains open for visitors, but there have been fewer people entering the park.

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