The Rim Fire near Yosemite National Park in California - now
180,000 acres burned and 20 percent contained - continues to hold
the full attention of water managers to the west in the San
Francisco Bay Area, which relies on a reservoir near the fire for 85
percent of its drinking water. But authorities say there is no cause
for alarm, at this early stage of the fire, about possible health
effects from ash that the smoke is dropping onto Hetch Hetchy
The water being delivered 160 miles downstream to Bay Area
residents remains safe, they say. One reason is that water drawn for
customers is 270 feet below the reservoir surface. Another is that
turbidity levels in the reservoir, being monitored by sensors 24
hours a day, are normal - exactly the same as before the fire
started burning. Moreover, the entire network of storing and
transporting water - from dams to concrete storage, to reservoirs
and pipes - has seen a $4.6 billion upgrade over the past 10 years,
just in time for a possible emergency such as this.
On top of that, contingency plans exist for delivering safe water
to customers, should the level of pollutants rise in Hetch Hetchy.
Those include filtering the water from the reservoir, if need be, or
simply using water from other unthreatened reservoirs.
"We are continuing to monitor the water 24/7, so if there is any
danger at all we will know immediately and switch to alternative
sources," says Alison Kastama, spokeswoman for the San Francisco
Public Utilities Commission (SFPUC). The two reservoirs that store
the Bay Area's remaining 15 percent of supply are right in the Bay
Area, in Alameda and San Mateo - far from the Rim Fire. "We are
shifting ample supplies to these other reservoirs just in case," she
What about concern that the real threat will come in the spring,
when runoff from rain and melting snow up in the Sierra Nevada will
carry residual ash on the ground into the water supply? Ms. Kastama
and others take issue with that assessment.
"One of the things that strikes me about the whole situation is
that none of the lands that are actually watersheds that run into
Hetch Hetchy have burned so far," says Jan van Wagtendonk, research
forester emeritus for the US Geological Survey's Yosemite Field
Station. Most of the watershed above the reservoir is granite, with
very few trees, he says, and the Rim Fire is unlikely to get to the
forested areas beyond.
"People tend to be alarmist, especially water people," says Dr.
van Wagtendonk. …