USING ENVIRONMENTAL TRACERS TO DEVELOP A CONCEPTUAL FRAMEWORK OF GROUNDWATER INFLOW INTO FARMINGTON BAY, GREAT SALT LAKE, UT

Great Salt Lake (GSL), UT is one of the largest and most ecologically important water bodies in North America. With record low lake levels in recent years, better understanding the water budget of Great Salt Lake is of utmost importance. While surface water inflows are relatively well understood and easy to quantify, estimates of groundwater inflow are very poorly constrained and have widely been estimated from water budget residuals. Original calculations attributed ~3% of total inflow to groundwater. Recent work has suggested higher inflow percentages, near 10-12%. The uncertainty and inconsistency in groundwater inflow estimates highlights the difficulty in quantifying subsurface flow without a conceptual understanding of the origin, flow paths, and discharge zones in the GSL catchment. Independent measurements are needed to constrain groundwater contribution in the water budget.

Environmental tracers, especially tritium (³H) and dissolved noble gases, are powerful tools for understanding the age and origin of groundwater flow, respectively. It has been demonstrated using ³H/³He age-dating and noble gas thermometry that in the Salt Lake Valley (south of GSL, where groundwater discharge into the Jordan River is known to be significant) that 1) groundwater flows from the mountains towards the Salt Lake Valley at a velocity of ~1 km per 5 years and 2) most groundwater samples have high recharge elevations (ie. came from the mountain block).

Preliminary data not only suggests similar trends, but also that significant quantities of fresh groundwater exist below Farmington Bay (southeast arm of GSL). Furthermore, all deep monitoring wells in Farmington Bay suggest high recharge elevations and relatively old age (some 1,000’s of years old), with an age-gradient of groundwater flow towards (and underneath) GSL already emerging. However, shallow wells installed in Farmington Bay suggest groundwater recharged while salty (likely from downward diffusion from GSL). Discrete areas of groundwater discharge into GSL have not been found yet. We aim to integrate these techniques with aerial thermal imagery, electrical resistivity, water level measurements, and other environmental tracers (major ions, salinity, CFC’s, SF6’s, δ¹⁸O, and δ²H) to constrain groundwater flow and develop a more robust conceptual framework of groundwater inflow to Great Salt Lake.