‘FOSSIL WATER’ MAY BE VANISHING
New study finds 7 percent of state’s drinking wells are tapping ancient water stores
A dinosaur bone. The footprint of a woolly mammoth. An ancient shell imprinted on a rock in your backyard.
These are the images the word “fossil” calls to mind. But, buried deep within the earth, there’s another kind of fossil you might not expect — ancient aquifers, created by rain and snow that fell more than 10,000 years ago. And unless the fossil water stores are better protected, scientists say, they may become a thing of the past.
New research on fossil water from Lawrence Livermore National Laboratory suggests that drinking wells that pump fossil water can’t rely on it being replenished — especially during times of drought.
“It’s just like taking gold out of the ground, out of a moun
tain,” said Menso de Jong, a groundwater management consultant at Kear Groundwater in Santa Barbara. “The gold is not going to grow back.”
The new Lawrence Livermore study found clear evidence that 7% of the 2,330 California’s drinking wells tested are producing fossil water — and 22 percent of the wells analyzed are pumping mixed-age water containing at least some ancient water. That means that many Californians are already using fossil water to shower, flush their toilets and irrigate their lawns without knowing it.
On the Central Coast, the Lawrence Livermore research team found fossil water in some of the deeper portions of the Salinas Valley’s aquifer system where the groundwater is not now being replenished through Monterey County’s water recy
cling programs.
Scientists say that further mapping out where fossil water is located and pinpointing the areas that rely on the ancient resource could help lead to better groundwater management and ensure that supplies are sustained to meet future needs.
If managers can determine how much is left, they can then ration it and work on strategies for replenishing the ancient wells.
Excessive agricultural and urban water use has depleted many of California’s aquifers, which serve as massive underground reservoirs. In some areas,
the problem is so severe that the land is subsiding — permanently in some cases.
California’s first- ever groundwater protection law, passed by the Legislature in 2014, requires local agencies to make their aquifers “sustainable” by 2042 at the latest. And that has increased the need for further understanding and mapping the worlds of trapped water. The new research will help identify where water is being pumped faster than it can be renewed — a critical step toward sustaining water resources to meet future needs.
Fossil water, or “paleowater,” is most commonly defined as water that seeped into the ground during the last Ice Age, when woolly mammoths roamed the earth. The water filled the porous cracks between rocks and grains of sand in a process known as “recharging.”
“Modern” groundwater also recharges. But because ancient hydrology was quite different from current conditions — in general, it was a lot cooler and wetter — the paleowater won’t be replenished for hundreds or even thousands of years.
Determining the age of water isn’t easy. The Lawrence Livermore research team, which also included scientists from Cal State East Bay and UC Santa Barbara, tested wells across the state using radioactive isotopes such as tritium.
Though tritium is a naturally occurring element, tritium levels rose in the last century with the advent of nuclear testing. Finding detectable levels of the isotope in water sources indicates to scientists that the water recharged in modern times as opposed to eons ago when levels were much lower.
Paleowater in the Golden State is more likely to be found in the dry south
western part of the Central Valley — between Los Banos and Lemoore — and in Southern California’s deserts in places such as Joshua Tree National Park and Coachella Valley towns like Palm Desert. This is because groundwater supplies are often naturally replenished in mountainous regions that get a lot of rain. In desert regions, however, the amount of rainfall isn’t enough to replenish the aquifers after the water is pumped to the surface.
Pumping fossil water is hardly new. Arid countries such as Yemen, Jordan and Libya have been using it for years to fill critical needs — but the ancient aquifers are now running frighteningly low.
Because fossil water fell from the sky thousands of years ago, there’s a greater risk of depleting the resource, scientists say.
“It’s kind of like a bank account,” said Ate Visser, a research scientist at Lawrence Livermore who co-authored the study on the finite nature of fossil water. “If you start withdrawing from your bank account but you have no income, at some point it’s going to run out.”
Knowing how much paleowater is left in a production well is not the only concern scientists have when it comes to the ancient water. A 2017 study published in the journal Nature Geoscience showed that wells that pump fossil water are also at risk for contamination.
“Even these ancient waters that tend to be tens or hundreds of meters underground are not safeguarded,” said Scott Jasechko, a water scientist at UC Santa Barbara who was the lead author of the contamination study.
“Just because you drill a deep well into fossil groundwater doesn’t mean the quality of that water is going to be pristine,” said
Jasechko, whose study argues that water managers should consider the risk of outside contaminants when ensuring the safety of paleowater.
The slow renewal of groundwater could affect whether homes, offices and stores are built in these areas in the future.
Areas that rely on paleowater could face building moratoriums if the water mining continues, said de Jong, who worked on the Lawrence Livermore study as a graduate student at UC Santa Barbara.
“There are some areas in these desert regions where it is very difficult now to get a permit to either drill a new well or really even to build a new house,” de Jong said.
Finding a way to mimic the natural recharge cycle, he said, might be the only way to stop the fossil water from eventually disappearing.
Visser suggests that California communities consider using treated flood water to replenish groundwater resources — an increasingly popular idea that is extremely costly and bound to face political opposition.
In addition, communities could prevent depletion of fossil water stores by tapping river water during the rainy season, Visser said.
Ultimately, water managers will need to ensure the water pumped out of California wells is renewed at a sustainable pace. And to do so, scientists say, there must be greater research about the water’s vintage and origins.
According to de Jong, “I don’t think there’s any debate at all that the system that humans have set up in California in the last hundred years will need some alterations in order to encourage more groundwater recharge.”