San Francisco's water supply may become cloudier over the weekend due to ash from the massive wildfire that's burning near Yosemite in an area that houses some of The City's hydroelectric power system.
And while the San Francisco Public Utilities Commission has sent some of The City's water supply farther downstream from the Hetch Hetchy Reservoir in Yosemite National Park, officials stressed Friday afternoon that there is no imminent threat to The City's water supply.
The Rim Fire grew to over 100,000 acres in size by early Friday, quadruple the size since Wednesday. Early Friday morning, the flames reached Yosemite National Park, and the blaze was burning in an area near city-owned Camp Mather by 8 a.m., according to officials with Cal Fire and the U.S. Forest Service, which are jointly managing the over 2,000 firefighters battling the fire.
Flames had spread northeast to within 2.5 miles of the Hetch Hetchy Reservoir. The dam and attendant powerhouses downstream also produce the electricity needed to power city buildings and Muni vehicles.
As a precaution on Monday, two of The City's three hydroelectric-producing powerhouses -- Kirkwood and Holm -- were powered down.
The fire burned through the areas where the powerhouses are located, and also burned through an area where 12.5 miles of high-voltage wires are located, SFPUC officials said Friday.
Of The City's three powerhouses, only the Moccasin powerhouse is still in operation. The Moccasin powerhouse has since Monday produced 50 of the 160 megawatts needed by The City daily; the other 110 megawatts has been purchased from the grid, SFPUC officials said.No cost estimate on the purchase was available Friday.
There is no way to know how badly damaged The City's power lines are at the moment, as fire officials are restricting access to the area. However, the Kirkwood powerhouse -- which is made of solid concrete -- is still transmitting information wirelessly, SFPUC officials said.
While no flame retardant is being dumped in the Hetch Hetchy watershed, and no fire-fighting aircraft are drawing from the reservoir to douse flames -- by request of SFPUC officials in order to protect the water quality -- The City's water supply may become cloudier as a result of the rim fire, officials said Friday.
Ash from the torched trees could put some "carbon" in The City's water, but at a level far below what's considered unsafe and possibly so low that no difference could be noticed.
As a precaution, the SFPUC has also pumped some of the water normally stored in Hetch Hetchy to reservoirs in San Mateo and Santa Clara counties in order to safeguard it from fire-related effects.