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

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

It is not difficult to find groundwater.

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

Groundwater makes up just over 30% of all freshwater on Earth, while almost 70% is trapped in glaciers and ice caps. Only a tiny percentage of the planet’s freshwater supply consists of free-flowing surface water.

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

It’s all the more important to understand this vital resource — especially in the drought-stricken West, where many communities, from Moab to Cedar City to California’s Coachella Valley, rely on underground aquifers.

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

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

(Francisco Kjolseth | The Salt Lake Tribune) Hydrologists place groundwater monitoring equipment near an amphibious vehicle used to navigate the Farmington Bay wetlands and which was also used to widen and maintain a channel for treated effluent from Davis’ Central Wastewater Treatment Plant, as pictured on Thursday , November 2, 2022. Thickets of invasive phragmites are choking the area which may dam the discharge and block movement of most wildlife.

Age dating is important because it helps municipalities and water districts understand long-term resource planning. You can see how long it took for the water to seep into the ground and if they are using more water than is being replenished by rain or snow. A popular analogy compares some communities’ water use to an overdrawn bank account. You can still take water, but if you spend more than your paycheck (i.e. charge through snow or rain), the reckoning will eventually come.

At this point, Solomon said, there are several fairly reliable geological tools for determining how deep and how full a subterranean aquifer is. “Much, much harder to understand is how much [water] actually recharges the system,” Solomon explained. “And therefore how much water can you capture before you start removing the water before using it as a non-renewable resource?”

This is where age assessment comes in, which can provide water utilities with some sort of blueprint. “A lot of dating work is to help people understand sustainable returns,” Solomon said.

The noble gas lab at the University of U. is one of about half a dozen around 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 is involved in ongoing research studying the Ogallala Aquifer in Central Nebraska and Farmington Bay on the southeastern shore of the Great Salt Lake where freshwater forms the Farmington Bay Wildlife Management Area.

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

The shiny, specialized mass spectrometer used in Solomon’s dating lab makes a chk-chk-chk-chk sound. “No one builds a machine like this,” Solomon said. The parts of the machine were custom made in the UK and Germany.

Most laboratory tests of the water Solomon are 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 thousands of times,” Solomon explained. But in 1963 an international ban on above-ground nuclear tests was ratified and enacted. The tritium concentrations decreased again.

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

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

There are other gases like sulfur hexafluoride (a potent greenhouse gas) that are increasing. Solomon’s lab uses carbon-14, considered by some to be the “most important isotope,” using extremely old water to this day.

Working with the United States Geological Survey, Solomon’s lab used this technique to determine the age of groundwater in the Utah-Nevada Great Basin, which is typically around 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 other researchers also studied the Glen Canyon Group aquifer, which the city of Moab depends 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 here has been shown to significantly improve our understanding of groundwater availability in a desert environment where water resources are scarce.” The evidence suggested that previous research “was overestimated [the] groundwater regime.”

Age dating found the water from the Moab City Springs to be between 2,000 and 3,000 years old, Solomon said. He said communities that rely on the aquifer would “withdraw approximately the amount of water that is returned to that system.” But if the city starts drilling more wells and drawing more water, they could start running a deficit.

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

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

“There is some utility to the tools that the USGS uses for geochemistry,” Williams said. “But I don’t think it’s critical to determining the amount of groundwater available to the Moab Spanish Valley.”

Spanish Valley, a development five miles south of Moab, has seen booming growth as Southeast Utah continues to attract tourists, outdoor enthusiasts and new residents. The need for water supply and sanitation has been the subject of policy and planning discussions for years.

Additional city and state studies suggest there is room for Moab to grow and use more water, Williams said.

Meanwhile, in Cedar City, another southern Utah community struggling with development and limited water resources, the issue of groundwater availability has veered into litigation. The Central Iron County Water Conservancy District argues that safeguards will ensure its Pine Valley groundwater pumping project doesn’t damage surface water sources, but neighboring Beaver County leaders are pushing back.

Such scenarios can make water supply issues moot, but Solomon, with his long career in groundwater research, takes a philosophical view of the world’s water supply. He often reflects on how communities “depend on something that happened in the past.”

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

This simple question “how old is this water” leads to many further and deeper investigations.

For example, how does climate change affect groundwater?

A warming planet, Solomon said, has changed the way groundwater systems are recharged. The timing of precipitation and whether there is sufficient snow or rain affects how much water ultimately seeps back into the ground.

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

For Solomon, understanding the past and how it changes is not just an abstract research discussion. In a time of prolonged drought, population growth and displacement, finding answers to these questions becomes increasingly urgent. How old is the underground water? Why the answer matters in the thirsty west

Justin Scacco

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