Reposted from the College of Science.
As a 10-year-old growing up in arid Granger, Utah, (now West Valley City), D. Kip Solomon spied a pipe stuck in the ground of his family’s backyard.
When he asked his father what it was, he was told it was a direct line to a vast underwater lake with an unlimited volume of water. Solomon was fascinated by the idea which raised many questions for him: Where did it come from? How long has it been there? And how did his father, who admittedly had “immense practical knowledge,” according to Solomon, know that?
Kip Solomon, University of Utah hydrogeologist.
“Well, he was wrong. Sort of,” said Solomon, who as a child may have been imagining an underwater lake that you could waterski on. “If you dug a hole, it’s not like an underground cavern or something. It was in a different context,” he concedes. But the groundwater is there, and it’s massive: 10 Lake Powells’ worth below just the Salt Lake Valley.
But that “different context” of his father’s claim of an underground lake, was something Solomon, recently recognized with the Hydrogeology Division of the Geological Society of America’s prestigious O. E. Meinzer Award, would learn about during the next three decades. Most recently, Solomon, now in a second tour of duty as chairman of the University of Utah’s Department of Geology & Geophysics, has been using environmental tracers to evaluate groundwater flow and solute transport processes in local- to regional-scale aquifers.
In particular, Solomon has developed the use of dissolved gases including Helium-3 (3He), Chlorofluorocarbons (CFCs) and Sulfur hexafluoride (SF6) to evaluate groundwater travel times, location and rates of recharge and the sustainability of groundwater resources. He constructed and operates one of only a few labs in the world that measures noble gases in groundwater, and his research results have been documented in more than 125 journal articles, book chapters, and technical reports.
Solomon’s lab in the Sutton Building looks like the sandbox of a dimly lighted playground straight out of a B-movie: an impressive array of copper tubes and steam punk-styled oxidized baubles, huge humming spectrometers, beakers and refrigerators, plunging samples to 10 degrees Kelvin.
“Minus 263 degrees,” Solomon explained over the humming of equipment. “That’s very cold, you know. And we have to do that to separate the noble gases, one from another.” Cryogenically separating these gasses is required to measure one thing at a time, and it is technology and equipment that also can break, frequently.
Copper tubes suck out the gases that are dissolved in the water specimen from which measurements of 3He are secured. Credit: Todd Anderson
“Imagine that you are cooling to minus 260 degrees and then warming to plus 30 or 40 degrees and you were doing that hundreds of times a day,” he said, two of his lab group Emily Larsen and Will Mace looking on. (“Will’s over there nervous that I’m gonna break something,” Solomon quipped as he continued the tour.) “It’s always temperature swings and so forth. And then just, you know, just cooling to the insulation that’s required to be able to cool to that temperature.”
It’s all part of the process of dating groundwater by measuring tritium, a radioactive isotope of hydrogen that decays in a half-life of 12 years or so, to 3He, a rare, stable and non-radioactive isotope of helium. In the soup of it all is Larsen, preparing specimens by eliminating extraneous gases and sealing them up, placing them on a shelf for six weeks and letting tritium decay to the stable noble gas of 3He which is then measured.
In addition to measuring tritium, the team deploys a procedure in nearby copper tubes that suck out the gases that are dissolved in the water specimen from which measurements of 3He are taken. It is the ratio of tritium to 3He3 that measures how long the water has been in the ground, that is, its age.
The Solomon lab’s findings paint a much more complex … and sobering picture of how depleted groundwater, overwhelmingly the largest volume of freshwater that’s available on Earth, gets recharged and how long it can take.
“I’m an engineer,” Solomon said, “so I’m always looking for solutions, but you can’t look for a decent solution until you really understand the problem.”
So, while that massive volume of water under the Salt Lake Valley does in fact exist, the rates at which water is recharged to the subsurface and moves through the subsurface of that reservoir is small and exceedingly difficult to measure due to variability that is “mind-boggling.”
That limited transfer is largely related both to climate and the amount of precipitation. But it’s also related to geology, “how well rocks and sediments are able to transmit water,” Solomon said, referring to permeability, a property of the Earth’s soil that first motivated his work. Of late, there is an accumulating literature about the age of water, another metric that impacts our understanding of transfer rates and might lead to new water management policies and the “solutions” that the engineer in Solomon is constantly scanning the substrate for.
Why study the age of water? “If you can measure how long it took for that water to go from where it got recharged, to where you’re collecting it, or to where it’s discharging, now you have a means, a different sort of method to evaluate groundwater flow systems.”
One thing is for certain in the world of hydrogeology: without even knowing it, you can easily use more groundwater than is being sustainably recharged. And it’s happening right now across the globe.
Read David Pace’s full story here.