How old is that water underground? Why the answer matters in the thirsty West

A U. of U. geophysicist determines the age of groundwater around the world, and how it affects supply and demand.

(Francisco Kjolseth | The Salt Lake Tribune) U. of U. graduate geoscience groundwater hydrology student Alex Engstrom, measures out a line of groundwater monitoring devices across a widened discharge channel for the central Davis sewer plant near Farmington Bay on Thursday, Nov. 3, 2022. Engstrom is in the process of measuring groundwater seepage that originates from a number of sources nearby with a primary look at levels of mercury.

This story is part of The Salt Lake Tribune’s ongoing commitment to identify solutions to Utah’s biggest challenges through the work of the Innovation Lab.

It’s not hard to find groundwater.

“It’s everywhere,” said Kip Solomon, a geology and geophysics professor at the University of Utah. “There’s no place on earth where you can’t drill a well and hit groundwater.”

Groundwater makes up a little more than 30% of the freshwater on earth, while nearly 70% is locked up in glaciers and icecaps. Only a tiny percentage of the planet’s freshwater supply is made up of freely flowing, surface level water.

What can be difficult, Solomon said, is finding “water that is of good quality, that’s not too salty. And it’s harder to find water where you can pump out large quantities.”

That makes understanding this critical resource all the more important — especially in the drought-stricken West where many communities, from Moab to Cedar City to the Coachella Valley, California, rely on underground aquifers.

“Drought is putting our water resources in the public eye,” Solomon said.

For decades, Solomon’s research has primarily focused on answering one important question: How old is this water?

(Francisco Kjolseth | The Salt Lake Tribune) Hydrologists place groundwater monitoring devices near an amphibious vehicle used to navigate the Wetlands of Farmington bay that has also been used to widen and maintain a channel for treated discharge from the central Davis sewer treatment plant, pictured Thursday, Nov. 2, 2022. Thickets of invasive phragmites choke the area, that can damn up the discharge and block the movement of most wildlife.

Age dating is important because it helps municipalities and water districts understand with long-term resource planning. They can see how long it took for the water to seep into the ground, and whether they are using more water than is replenished by rain or snow. A popular analogy likens some communities’ water usage to an overdrawn bank account. You can keep taking water out, but if you’re spending more than your paycheck (i.e. recharge from snow or rain), the reckoning eventually comes.

It’s all about the recharge

At this point, Solomon said, there are several fairly reliable geologic tools available to determine how deep and how full an underground aquifer is. “What’s much, much harder to understand is how much [water] is actually recharging the system,” Solomon explained. “And therefore, how much water can you extract before you start mining the water, before you start using it as a non-renewable resource.”

That’s when age dating comes into play – which can provide a planning blueprint of sorts for water providers. “A lot of dating work is to help people understand sustainable yield,” Solomon said.

The Noble Gas lab at the U. of U. is one of roughly a half dozen in the world, he said, that can “determine how long the water has been in the ground.” People send Solomon samples from all over the world. He’s involved with ongoing research studying the Ogallala aquifer in Central Nebraska and in Farmington Bay on the southeastern shore of the Great Salt Lake, where fresh water makes up the Farmington Bay Wildlife Management Area.

(Francisco Kjolseth | The Salt Lake Tribune) Alex Engstrom, a University of Utah graduate student in geoscience groundwater hydrology, installs a monitoring device used to measure groundwater seepage in Farmington Bay on Nov. 3, 2022.

The gleaming, specialized, mass spectrometer used for age dating in Solomon’s lab makes a chk-chk-chk-chk sound. ���Nobody builds a machine like this,” Solomon said. The machine’s parts were custom made in the United Kingdom and Germany.

Most of the water Solomon’s lab tests is less than 100 years old. The age of the water is determined by measuring tritium, a radioactive isotope of hydrogen.

Tritium serves as a useful marker because in the 1950s, the heyday of nuclear weapons testing, the concentration of tritium in the atmosphere “increased by many thousands of times,” Solomon explained. But in 1963 an international ban on above ground nuclear tests was ratified and enacted.Tritium concentrations, in turn, declined.

Solomon measures the amount of tritium in a water sample and its “daughter product”– helium three.

“If we take the sample and we measure five tritium atoms and five helium three atoms,” Solomon explained, “we know that the water is 12 years old.”

There are other gasses, such as sulfur hexafluoride (a powerful greenhouse gas), that are increasing. Solomon’s lab uses carbon-14, considered the “most important isotope” by some, to date extremely old water.

Age dating in Utah’s desert communities

Working with the United States Geological Survey, Solomon’s lab used this technique to figure out the age of groundwater in the Utah-Nevada Great Basin, which tends to be roughly 40,000 to 50,000 years old. The team is still trying to better understand the relationship between surface water and groundwater in Nevada’s Great Basin National Park, Solomon said.

Solomon and fellow researchers also examined the Glen Canyon Group aquifer, which the city of Moab relies on for its culinary water supply. A 2020 paper published in the Journal of Hydrology concluded that “the use of a combination of environmental tracers and groundwater geochemistry has been shown here to significantly improve our understanding of groundwater availability in a desert environment where water resources are scarce.” The evidence suggested that previous research “overestimated [the] groundwater budget.”

Age dating revealed that the water coming from the Moab City Springs was between 2,000 to 3,000 years old, Solomon said. He said the communities relying on the aquifer are “withdrawing about the amount of water that is being recharged to that system.” But if the city starts drilling more wells and taking out more water, they could start drawing a deficit.

Age dating water “speaks to the long term sustainability of groundwater systems,” Solomon said.

There are some differences of opinion on that point, said Moab City Engineer Chuck Williams, who oversees the city’s water infrastructure. “A lot of good work has been done in the last five years,” he said.

“The tools that the USGS use for geochemistry, there’s some use in that,” Williams said. “But I don’t think it’s definitive in determining the amount of groundwater that’s available for the Moab Spanish Valley.”

Spanish Valley, a development 5 miles south of Moab, has been booming in growth as southeastern Utah continues to draw tourists, outdoor enthusiasts and new residents. Water supply and sewer needs have been topics of policy and planning discussions for years.

Additional studies by the city and state have come to imply that there’s room for Moab to grow, and to use more water, Williams said.

Meanwhile, in Cedar City, another southern Utah community wrestling with development and limited water resources, the issue of groundwater supply has bubbled into a legal battle. Central Iron County Water Conservancy District argues safeguards will ensure its Pine Valley groundwater pumping project won’t harm surface water sources, but neighboring Beaver County leaders are pushing back.

Such scenarios can make questions around water supply contentious, but Solomon, with his long career of groundwater research, looks at the world’s water supply philosophically. He often thinks about how communities are “depending on something that happened in the past.”

(Francisco Kjolseth | The Salt Lake Tribune) An amphibious vehicle is used by hydrologists to reach areas of study in Farmington Bay, choked by invasive thickets of phragmites on Thursday, Nov. 3. 2022.

That simple question of ‘how old is this water,’ spirals into many more, and deeper inquiries.

For example, how is climate change impacting groundwater?

A warming planet, Solomon said, has been shifting the way groundwater systems are recharged. The timing of precipitation and whether adequate amounts of snow or rain fall influence how much water ultimately seeps back into the ground.

“We don’t yet have definitive results to say that recharges decreased by ‘X’ amount,” Solomon said. “But we’re absolutely concerned about that.”

Understanding the past, and how it’s changing, isn’t just an abstract research discussion for Solomon. In a time of persistent drought and population growth and shifts, finding the answer to these questions is increasingly urgent.