Published: June 28,2016
California's parched Central Valley in 2014. (Stuart Rankin/NASA/flickr)
But
tapping that water, locked thousands of feet beneath the ground, will
be expensive and comes with an enormous risk — it could cause the
valley floor to sink, according to the study, published Monday in the
Proceedings of the National Academy of Sciences. Sinking land in the
Central Valley is threatening roads, homes and other infrastructure, and
reduces the amount of water some aquifers can hold.
“It’s not often that you find a ‘water windfall,’ but we just did,” said study co-author Rob Jackson,
an earth system science professor at Stanford University. “California’s
already using an increasing amount of groundwater from deeper than
1,000 feet. Our goal was to estimate how much water is potentially
available.”
Climate change is exposing the state
to a greater threat of drought, reducing the amount of water available
for farming and drinking as higher temperatures evaporate reservoirs.
More precipitation is expected to fall as rain instead of snow in
California as the world warms, forcing the state to find new ways to
store rain water for municipal and agricultural use.
To stave off losses during its four-year drought, California has relied on groundwater to irrigate its farm fields. So much groundwater is being used that the water table has fallen by 50 feet in some places in the Central Valley, and the valley floor is sinking, or subsiding, as aquifers are depleted.
Land
subsidence, which has been occurring in the valley for decades because
of groundwater pumping, has accelerated to two inches per month in some
places, according to NASA. Sinking land threatens roads, bridges, aqueducts, buildings and other infrastructure as the land collapses beneath them.
The California drought has forced cities to cut back on water use. (Kevin Cortopassi/flickr)
Most
of the groundwater comes from aquifers less than 1,000 feet deep.
Deeper aquifers are usually considered too salty to be used for drinking
or irrigation, requiring costly desalination and drilling operations to
access them.
Analyzing water data gathered from
oil and gas wells across eight Central Valley counties, the Stanford
researchers show that there are about 2,700 cubic kilometers of
accessible fresh or brackish water locked in the Central Valley’s deep
underground aquifers. That’s almost triple the 1,020 cubic kilometers of
freshwater that had been previously estimated.
Farming
in California consumes between 25 million and 33 million acre-feet of
water annually, or between 31 and 40 cubic kilometers of water,
according to a 2015 Congressional Research Service report. A cubic kilometer of water is roughly equivalent to 1.3 times Los Angeles’ annual water use.
Some of the water that Jackson’s team found is considered brackish — containing low levels of salt — but it could be affordably desalinated, the study says.
“States
such as Texas and Florida, and countries, including China and
Australia, are already desalinating brackish water to meet their growing
water demands,” the study says. “Accounting for deep but relatively
fresh groundwater can substantially expand California’s groundwater
resources, which is critical given the state’s current water shortages.”
Additional
research is needed to determine how much tapping the water would cause
the valley floor to sink and how oil and gas development, which is
common in those deep aquifers, could contaminate the water, especially
from fracking, according to the study.
“We're not advocating running out and drilling lots more groundwater wells,” Jackson
said. “The Central Valley's been in denial about groundwater overdrafts
for years. We need to consider ground subsidence. We also need to think
about oil and gas activities directly in and around freshwater
aquifers. Is that the best use of the resource long term?”
California’s
water agency, the State Department of Water Resources, is concerned
about the long-term implications of possibly using — and using up — a
newly found reserve of freshwater.
“Understanding
the total aquifer capacity is valuable from a technical standpoint, but a
more useful estimate would be how much of the aquifer can we truly
utilize before we experience significant impacts to surrounding
agricultural, urban and domestic water users, to public infrastructures,
to the environment and to the aquifers’ ability to recharge in a
reasonable time frame,” said Lauren Hersh, spokeswoman for the
California Department of Water Resources’ Sustainable Groundwater
Management Program.
Leonard Konikow,
an emeritus U.S. Geological Survey groundwater scientist and author of a
2013 federal government report on groundwater depletion in the U.S.,
said deep underground freshwater may be too expensive for many in
California to access.
“In a severe drought, such
deep drilling for water might be justified for municipal or industrial
supplies, but I can’t imagine that the cost would ever be justified for
agricultural purposes,” he said.
But Jackson said deep freshwater is a largely untapped and little-understood resource.
“It’s a huge pool of water,” Jackson
said. “Some companies and towns are already pumping deep groundwater.
It’s a little more expensive to use because of the pumping costs, but
people are already doing it. Remember, too, that private landholders
often have few restrictions on what they can pump.”
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