A team of geologists drilled through strange formations dotting the lake’s drying playa, and were surprised by what they found.
Farmington Bay • The assumption was that the water underlying the Great Salt Lake was salty, just like the lake itself.
But as scientists dug deeper over the last year, they found something underneath Farmington Bay that defied expectations. A huge freshwater aquifer likely extends hundreds, if not thousands of feet deep, recent exploration has found. That means fresh groundwater could reach as far beneath the Great Salt Lake’s surface as the Wasatch Mountains rise above it.
“That’s the magic of this basin and range topography,” said Bill Johnson, a professor of geology and geophysics at the University of Utah.
Fresh groundwater probably exists all around the lake, including its drier western shore, Johnson said. It may even pool below Gilbert Bay, the main body of the lake west of Antelope Island. And while the aquifer probably isn’t a viable new supply for the Wasatch Front’s rapidly growing cities, it could protect its residents from a growing threat to public health.
“For the purpose of wetting the playa,” Johnson said, “and trying to keep it from getting too dusty, it’s a great resource.”
That’s because the groundwater is under so much pressure, it flows to the surface naturally without requiring any pumps or power. Wells could potentially flow to drip irrigation lines and dampen dry hot spots that release dusty lakebed pollution when the wind blows. Or they could help reform a salty crust that keeps the lakebed’s sediment from becoming airborne.
“What we’ve discovered is, it’s pretty easy to reset the crust with water,” said Kevin Perry, a professor of atmospheric studies at the U., “and it doesn’t take a lot of water to do it.”
Johnson first suspected freshwater might be seeping upward to the Great Salt Lake playa after studying aerial images and noticing strange dark circular spots dotting its growing exposed lakebed.
After studying aerial imagery, University of Utah geology professor Bill Johnson noticed dark, circular "round spots" on the Great Salt Lake's exposed lakebed that he suspected were clues that fresh water was seeping to the playa surface from below. Two of these round spots are seen in this recent aerial image of Farmington Bay.
Last fall, Johnson and his team realized the round spots were dense colonies of phragmites – a water-guzzling, invasive reed that popped up in the Great Salt Lake’s wetlands after calamitous flooding in the 1980s.
He tapped funding and expertise from the Utah Geological Survey and U.S. Geological Survey to explore further.
Using a combination of airboats when the bay was inundated with a few inches of water and bikes when the lakebed was dry, Johnson and his students have traveled miles across Farmington Bay to reach the remote and mysterious round spots. They hacked corridors through the phragmites thickets until they reached the heart of the rounds, then augured wells by hand.
Consistently the groundwater found at the center of the round spots was the freshest, getting saltier and saltier the more they moved to the edges, like a bullseye.
On a particularly sweltering day in June, the water at the center of “Round Spot 10″ was so fresh Johnson’s equipment wasn’t calibrated to measure it.
There are hundreds of these round spots dotting the lakebed, Johnson said, and he’s confident they all formed around fresh water.
“Statistically speaking,” the professor said, “four of the four we checked have fresh water. So do I need to check more? Not necessarily.”
The researchers said they have concerns about rapidly growing communities on the Wasatch Front learning of a potentially new, and possibly extensive source of freshwater beneath their imperiled neighboring lake. The wetlands that play a vital role in the Great Salt Lake’s ecosystem likely also depend on fresh, pressurized water seeping to the surface.
“It’s really complicated system,” said Hugh Hurlow, a hydrogeologist with the Utah Geological Survey, “and there are trade offs, and maybe unintended consequences, of doing anything with the lake.”
Additional new research shows groundwater plays an important role in filling the lake itself — about 10% of the Great Salt Lake’s water comes from groundwater, Hurlow said.
Pressure builds as underground water migrates from dense mountain blocks to the lowest point in the basin – the Great Salt Lake – and slowly fills porous valley sediments called basin-fill deposits. A shallow brine layer of groundwater and less permeable material acts as a lens preventing the freshwater from surfacing, but in certain spots, it makes its way up.
That’s what allowed water to flow to the surface without pumping when Johnson and his team augured their wells in the round spots.
“As long was we poke a hole in it,” Johnson said, “any well over 30 feet [deep], it’ll flow up.”
But both Hurlow and Johnson said the aquifer below the lakebed likely isn’t viable for municipal or industrial use.
“This isn’t going to be some water resource that a community develops,” Johnson said. “The sediments are too tight.”
It took some of their wells several days to refill after sampling, Hurlow said.
“What that means is the flow within the aquifer there is very, very slow,” he said. “It would not translate well to some kind of [municipal] production.”
Gov. Spencer Cox issued a proclamation in November 2022, when the lake hit a record-low elevation, closing most of its basin to new water rights appropriations. He does allow for some exceptions, however.
Research of the round spots and the groundwater beneath them was paid for with a portion of a $315,599 grant from the Great Salt Lake Commissioner’s Office to study the role of groundwater in sustaining the Great Salt Lake and its wetlands.
