University of Utah researchers have identified an extensive freshwater system beneath Farmington Bay and northern Antelope Island, sections of the Great Salt Lake. Utilizing airborne electromagnetic (AEM) surveys, the study mapped freshwater-saturated sediments extending to depths of 3 to 4 kilometers.
This discovery, published in Scientific Reports, represents the first successful detection of freshwater beneath the lake's conductive saltwater layer using this technology and suggests potential strategies for addressing dust pollution resulting from the lake's receding levels.
Discovery Details
The research team, led by geophysicist Michael Zhdanov and including hydrologist Bill Johnson, identified the freshwater reservoir beneath Farmington Bay and Antelope Island, located along the Great Salt Lake's southeastern margin. The study indicates that freshwater permeates sediments up to four kilometers (approximately 10,000 to 13,000 feet) deep beneath the lake's surface.
Observations of circular mounds, ranging from 50 to 100 meters across and covered in phragmites reeds, on the dried lakebed of Farmington Bay prompted the investigation. These mounds indicated the presence of groundwater emerging under pressure beneath the surface.
Research Methodology
The study employed airborne electromagnetic (AEM) surveys conducted via a helicopter equipped with electromagnetic technology. These surveys involved flying 10 east-west lines, covering 154 miles across Farmington Bay and northern Antelope Island. The AEM technology measured electrical resistivity, enabling researchers to differentiate between resistive freshwater and conductive saltwater layers.
Researchers found that one reed-covered mound was located directly above a point where freshwater was rising through a break in an impermeable layer beneath the lake. To create detailed 3D images of the subsurface, the CEMI (Consortium for Electromagnetic Modeling and Inversion) research group developed a method combining AEM data with additional magnetic measurements. This technique produced a tomographic model that extends deep beneath Farmington Bay, revealing geological and hydrological structures. Magnetic data inversion indicated a relatively shallow basement structure (less than 200 meters deep) beneath the playa that sharply descends to depths of 3 to 4 kilometers under one of the phragmites mounds, signifying a major structural boundary.
Key Findings and Hydrological Insights
Michael Zhdanov stated that the research represents the first successful application of AEM technology to detect freshwater beneath the Great Salt Lake's conductive saltwater layer. The study mapped the spatial extent of the freshwater and estimated the depth of water-saturated sediments by identifying the underlying basement structure. This data can aid in calculating the potential total volume of the freshwater reservoir.
Hydrologist Bill Johnson noted that the freshwater appears to be moving towards the lake's interior, rather than exclusively along its edges. This pattern deviates from typical hydrological expectations, which suggest denser brine would occupy the entire volume beneath the lake, with freshwater confined to the periphery. The current data indicates a deep volume of freshwater entering beneath the saline lens.
Context and Potential Applications
The research was initiated against the backdrop of the Great Salt Lake's significant shrinkage, having lost over half its size since 1986. This reduction has exposed approximately 800 square miles of lakebed, which has become a source of dust pollution containing metals.
Researchers are investigating whether this artesian groundwater could be utilized to wet dust hotspots in critical areas. A primary objective is to determine if the freshwater can effectively mitigate dust without substantially altering the overall freshwater system. The study highlights the importance of understanding the beneficial effects of this groundwater before considering any extraction.
Future Research
The current study covered a segment of the lake. Researchers are seeking funding to expand their groundwater studies to cover a larger portion of the Great Salt Lake, which spans an area of 1,500 square miles. A comprehensive survey would involve using AEM to determine saline layer thickness and freshwater starting depth, along with magnetic data to ascertain the depth of the basement. Such an expanded survey is considered necessary to fully understand the lake's subsurface hydrological system.
The findings from this research, funded by the Utah Department of Natural Resources, are expected to inform regional water management decisions and could potentially assist in locating freshwater resources beneath other terminal lakes globally.