Officials Discount Risk to Drinking Water from Rim Fire near Yosemite, So Far
Wood, Daniel B., The Christian Science Monitor
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 Reservoir.
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 says.
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. …