How Groundwater Contributes to Great Salt Lake
by Erin Brinkman and Hugh Hurlow
Great Salt Lake, UGS groundwater monitoring sites, and major streams.
Groundwater plays an important but often overlooked role in the Great Salt Lake (GSL) watershed system. Groundwater moves in underground aquifers from the surrounding mountains and valleys toward the lake, providing a steady source of supply that supports lake levels, wetlands, stream flow, springs, and water quality. Recent work revealed that groundwater flow to the lake is more significant than previously recognized, making it an important part of GSL’s water system. GSL is a terminal basin for both surface flow and groundwater, meaning no stream flow leaves the lake basin and groundwater moves towards GSL from all directions within its watershed. Groundwater in the GSL watershed is also used extensively for drinking water, agriculture, industry, and mining. Therefore, GSL’s condition reflects the climate and hydrogeologic variations as well as the human uses surrounding it.
Over the past decade, concerns about the ecological and economic health of GSL have grown among scientists, community members, and policymakers. Discussion has focused on declining lake levels, which has led to increasing salinity, additional exposed lakebed and dust generation, loss of wetlands and bird habitat, and challenges for the mineral extraction and brine shrimp industries. Stress on the groundwater system, including drought and increased groundwater pumping, has caused water-level declines in wells and springs around the lake. The need to better understand the role of groundwater in these important and complicated issues is noted in two key initiatives for long-term planning to sustain GSL and its benefits: the Great Salt Lake Strategic Plan and the Great Salt Lake Basin Integrated Plan.
The well configuration for our monitoring sites allows groundwater levels and chemistry to be measured over specific depth ranges in the basin-fill aquifer. The diagram does not represent the stratigraphy at any particular site; the depth and thickness of fine-grained materials varies from site to site.
Recognizing the need for better information about the role of groundwater, the Utah Geological Survey (UGS) began studying how groundwater flows into GSL during the mid-2010s. UGS researchers compiled existing data on water chemistry, spring flows, and groundwater levels around the GSL perimeter. We discovered a significant lack of data for the lake’s marginal wetlands, shoreline, and dry lakebed, mainly because these areas had been underwater for decades or had not yet experienced troubling groundwater declines. Now these areas are exposed, creating a new opportunity for the UGS to obtain data directly from the exposed lakebed, subsurface, and its margins.
To address this data gap, the UGS and partners installed the GSL Groundwater Monitoring Network, consisting of nine new monitoring well sites, each with several wells screened (open to the aquifer) at different depths (nested). The first group of wells were installed in 2023–24 near Farmington Bay in collaboration with the University of Utah, and the resulting data contributed to three master’s theses. The UGS installed the next set of wells in 2025–26 on the southwest, northeast, and northwest corners of GSL. During installation of these nested wells, we collected sediment cores up to 100 feet deep at each site that provided important data on the chemistry of the pore water and sedimentation history at the site.
The nested wells are open to aquifers at multiple depths at each site, allowing us to observe how groundwater levels and water quality vary vertically beneath the surface. The data collected from these wells improve our understanding of groundwater flow and geochemistry, provide subsurface information needed to calibrate groundwater flow models, and establish a long-term monitoring network to evaluate the effectiveness of future water management and conservation efforts.
The Farmington Bay wells demonstrated that below 30 feet depth, groundwater is less saline and produces flowing (artesian) wells under “confined” conditions (the aquifer is between layers of clay or impermeable rock). Detailed water chemistry analyses showed that the fresh groundwater below Farmington Bay entered the aquifer 15 to 20 miles to the east along the Wasatch Range front and took more than 100 years to reach its present location. This fresh groundwater reaches the surface in places as circular upwelling features (“round spots”). Antelope Island is a fault-bounded structural block that forms a barrier to westward groundwater flow toward the south arm of GSL, unlike the southern, western, and northern margins where groundwater may flow with less restriction toward the lake center.
Along the GSL eastern margin, groundwater moves upward from the deeper confined aquifer toward the land surface and also moves laterally within the shallow unconfined basin-fill aquifer where it helps support wetlands and streams. This groundwater flow is essential to ecological health and is vulnerable to depletion from groundwater pumping, surface pollution, and consumption by the invasive plant Phragmites (see Survey Notes v. 58, no. 1 and PI-108, https://doi.org/10.34191/PI-108).
Schematic diagram showing how groundwater flows from the Wasatch mountains to GSL. Groundwater resides in, and flows through, pore spaces between sediment grains in the Wasatch Front basin-fill aquifer (permeable sand and gravel). Precipitation, snowmelt, and stream flow soak into the ground and replenish the aquifer, a process called recharge. Most of this recharge occurs near the mountain front, and the groundwater flows downward and horizontally toward GSL as illustrated by the blue arrows. Near the lake, groundwater moves toward the land surface and helps support wetlands and streams along the eastern shore.
Since 1956, the height of water in flowing wells near and within the wetlands along the GSL eastern shore has dropped by more than 45 feet due to groundwater pumping to the east, reducing their flow to a mere trickle. This effect is widespread—groundwater levels have decreased by more than 50 feet during the past 70 years along much of the Wasatch Front.
Changes in a water table caused by groundwater pumping. The top diagram illustrates an aquifer and well configuration before pumping, and the bottom diagram illustrates changes to the water table due to pumping. A previously flowing well no longer flows, and the root zone of phreatic vegetation may be dewatered.
Groundwater pumping from the basin-fill aquifer creates cone-shaped areas of lowered groundwater levels, known as cones of depression, around heavily pumped wells. These cones of depression may extend over large distances, reducing groundwater flow to springs, wetlands, streams, and other wells. Although groundwater entered the aquifer more than 100 years ago, groundwater levels still respond to present-day pumping. Lowering the pressure in an aquifer drops water levels far faster than the water can be replenished from sources in the mountains, so even century-old groundwater levels fall in response to modern pumping.
Groundwater conditions around the rest of GSL likely vary significantly compared to the Farmington Bay area. Differences in precipitation and groundwater recharge rates, and aquifer composition result in variable groundwater flow and chemistry. The amount of potential recharge to the groundwater table from precipitation varies significantly around GSL because the mountains to the east and south of the lake receive a much higher amount of precipitation than those on the west side. Groundwater chemistry reflects chemical reactions with minerals in sediments that compose the basin-fill aquifer, which vary around the lake. Input of geothermal fluids rising along faults also causes local variations in groundwater chemistry. Preliminary data from our new wells on the north, south, and southwest lake margins show a range of groundwater chemistry and groundwater levels, and differences in salinity with depth compared to Farmington Bay. To fully understand groundwater processes around GSL, we are analyzing data from the wells and sediment cores collected during installation of our monitoring wells, and we are preparing the data for release on the online UGS Groundwater Monitoring Portal.
Many important questions remain about groundwater’s role in sustaining GSL ecology and water levels. These include how the permeability of subsurface sediments shapes groundwater flow rates and paths; how declining groundwater levels affect flow rates toward GSL and overall lake levels; how much groundwater reaches GSL indirectly through streams that flow into the lake; and how much groundwater flow sustains wetland water supply and habitat. The newly established groundwater monitoring network, combined with continued research, will help improve our understanding of these processes and provide the data needed to answer these questions in the future. A better understanding of groundwater flow into the GSL will help managers and decision-makers as they seek opportunities to restore lake levels and wetlands habitat.
For more information and references, please see the Great Salt Lake page of the online UGS Groundwater Data Hub.
