Study says ‘fossil water’ heading toward extinction
Report indicates 7% of California’s drinking wells already are tapping into ancient groundwater aquifers
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.
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 managers of 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 mountain,” said Menso de Jong, the study’s lead author. “The gold is not going to grow back.”
The Lawrence Livermore study found evidence that 7% of the 2,330 California’s drinking wells tested are producing fossil water, and 22% of those wells are pumping mixed-age water containing at least some ancient water. That means that many Californians already are using fossil water to shower, flush their toilets and irrigate their lawns without knowing it.
Scientists say that further mapping where fossil water is located and pinpointing the areas that depend 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 fossil water 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 sinking — permanently in some cases.
California’s first groundwater protection law, passed by the Legislature in 2014, requires local agencies to make their aquifers “sustainable” by 2042 at the latest. 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 out of aquifers faster than it can be renewed, which is 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 tens of thousands of years ago — 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 southwestern part of the Central Valley and in Southern California’s deserts, including Joshua Tree National Park and Coachella Valley cities such as Palm Desert. This is because groundwater supplies are often naturally replenished in mountainous and coastal regions that get a lot of rain. In desert regions, the amount of rainfall isn’t enough to replenish the aquifers after the water is pumped to the surface.
Because the Bay Area largely relies on surface water reservoirs such as Hetch Hetchy for drinking water, the region doesn’t have as many drinking water wells, said Ate Visser, a research scientist at Lawrence Livermore who coauthored the study on the finite nature of fossil water. Santa Clara County has by far the most wells of the Bay Area counties, he said, but very few of them are classified as “fossil.”
In coastal counties such as Santa Cruz and Monterey, the typically wet winters, “combined with the smallish aquifers, don’t create the kind of conditions that produce a lot of fossil groundwater,” Visser said.
In addition, researchers note, some coastal counties are spending hundreds of millions of dollars on projects aimed at replenishing their aquifers with highly treated wastewater.
Pumping fossil water isn’t new. Arid countries such as Yemen, Jordan and Libya have been using it for decades to fill critical needs, but ancient aquifers in those countries are now running frighteningly low.
Scientists say that because fossil water fell from the sky thousands of years ago, there’s a greater risk of depleting the resource.
“It’s kind of like a bank account,” Visser said. “If you start withdrawing from your bank account but you have no income, at some point it’s going to runout.”
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. He’s now a groundwater management consultant.
“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 more California communities consider using treated flood water to replenish groundwater resources. Communities also could prevent depletion of fossil water stores by tapping more river water during the rainy season, he said.
Ultimately, water managers will need to ensure that the water pumped out of California wells is renewed at a sustainable pace. And to do that, scientists say, there must be greater research about the water’s vintage and origins.
“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,” de Jong said.