Update: PUC lays out the options. See end.
The quality and clarity of Hetch Hetchy water have long been bragging points for San Franciscans, for whose benefit the pristine Yosemite valley was dammed and flooded.
Well, a massive out-of-control fire can change all of that -- especially since Hetch Hetchy is one of the few large-scale water systems not equipped with a filtration system. In the short-term Public Utilities Commission officials have shunted water into supplemental reservoirs before ashes befoul the source. In the long-term, however, as rainfall carries ash and detritus into the watershed, the city may be facing problems without easy, or even apparent, solutions.
Spreck Rosenkrans is a water expert and director of policy at Restore Hetch Hetchy. He emphasizes that the highest priority is putting out the fire quickly to save lives and property, and protecting San Francisco's water and power systems.
But, after that, San Francisco's problems could be legion.
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San Francisco's PUC had understandable trepidations about installing a filtration system -- a 2006 state estimate pitted it at $310 million to $515 million. That was probably low, and it'd only be more expensive now. Instead of being screened, Hetch Hetchy water is treated with ultraviolet beams. That's fine for most people, but several strains of bacteria problematic for HIV or AIDS patients are not eradicated.
Soon, however, the general population may have problems as well.
San Francisco, Rosenkrans notes, has the ability to filter water coming from its East Bay and Peninsula reservoirs with plants in Sunol and near the Crystal Springs reservoir. But Hetch Hetchy water usually contributes 85 percent of the system's supply. "The filtration plants have never faced up to the challenge of having a lot of stuff in the water," Rosenkrans notes. "They don't have the filtration capacity measured in millions of gallons per day to meet summer demand."
PUC director Harlan Kelly has said that San Francisco has lined up six months worth of reserve water. If ash overwhelms the water supply, he says, it will have to be filtered -- though he didn't know how much that would cost.
Rosenkrans is additionally uncertain how that would work, let alone how to pay for it. "There's no time to build filter plants. If they are required to filter the entire supply, they'll have to use the existing plants -- and, hopefully, that will happen after summer when demand is lower," he says. "If ashes get in the water, they might have to ask people to cut back on use and bring in water" from other systems.
Multiple calls to PUC officials have not yet been returned; there is, after all, a wildfire burning.
Update, 3:20 p.m.: PUC spokesman Charles Sheehan says that, as noted in the article above, there are filtration capabilities at one or more PUC plants. It is uncertain, however, just how much water these plants can filter. If too much ash found its way into the system, Sheehan says, it would necessitate switching to a different supply of water.
The largely completed $4.6 billion Water Safety Improvement Plan has eased this, he says. Inter-connections with water systems in the East Bay and on the Peninsula were established as contingencies for just such a situation, Sheehan says.
Finally, he notes that the Hetch Hetchy system has not been measured as any dirtier than prior to the fire. In fact, the threshold for requiring filtration would require a measured turbidity 25 times the current level.