By Paul Kozakiewicz
Starting in March, groundwater held in a huge underground
aquifer under the west side will be pumped out and blended with
water from the Hetch Hetchy Reservoir in the Sierra Nevada
The $66 million plan, approved by the SF Public Utilities
Commission (PUC), calls for up to 1 million gallons of groundwater
to be blended in the Sunset Reservoir this year. That would
be three percent of the total water volume going to city customers.
The pumping would be ramped up over the next four
years to about five million gallons of water a day, or up to 15
percent of the water delivered to city customers. The PUC also
sells water to numerous California cities, which will continue
to receive unadulterated water.
Six wells have been dug to deliver water to the Sunset
Reservoir. There are two in the Outer Sunset District, two in
Golden Gate Park, one in the Outer Richmond and one at
The well at the West Sunset Playground has a design with
features that will allow it to serve as an emergency drinking
water supply. It can be connected to a generator for backup power, disinfect water and be
connected to a fire hydrant for filling trucks.
The well water will have to be treated with chemicals to balance
the water’s acidity and to negate excessive nitrates and the
minerals calcium, magnesium, sodium and bicarbonate.
Nitrates, which come from leaking sewage pipes and fertilizer
runoff, are at levels above state standards.
The blended water will be “harder,” containing more total
minerals, or total dissolved solids (TDS). The current water
being delivered contains 40 to 45 TDS, whereas the blended water
will contain 70 to 120 TDS. The water will have increased levels
of calcium, magnesium and bicarbonate.
According to experts, the harder blended water could taste
different and make a difference in the making of coffee, beer and
some baked goods, like bagels and bread. Some items would
fare better with the blended water, like hoppy beers, and some
would fare worse, like pilsner beers, which require soft water.
The change could give dough more backbone, but could also
make it tougher and limit fermentation.
The extracted groundwater will be treated with chlorine to
kill dangerous microbes and sodium hydroxide to lower its
acidity. Hetch Hetchy water also gets treated with doses of chlorine
The PUC claims the underground water is needed for a
growing Bay Area, because the federal government might require
more water for the state’s rivers, and also in case of an
emergency that disrupts the water supply line from the Sierra,
like a major earthquake.
According to the PUC’s website, in a drought, the groundwater
blend will be distributed throughout the entire City.
According to the PUC, drinking the aquifer water without
blending it with Hetch Hetchy
water could create a health risk
because of the high levels of nitrates
in the aquifer water.
According to a recent story in the SF Chronicle, the chief hydrologist
for the PUC project, Jeff Gilman, said, “The nitrate
would only be a concern if you were serving that water directly,
but that’s not our plan.”
The underground aquifer is about 400 feet below ground level.
Wells have been dug to monitor it in case of saltwater intrusion
from the Pacific Ocean.
For more information, go to
the website at http://www.sfwater.org.