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 GSL is critical. While surface water inflows are relatively well understood and easy to quantify, estimates of groundwater inflow are very poorly constrained. 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.

Environmental tracers, especially tritium (³H) and dissolved noble gases, are powerful tools for understanding the age and origin of groundwater. 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 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 suggest high recharge elevations and relatively old age (some 1,000’s of years old, potentially from regional groundwater flow), and an age-gradient of groundwater flow moving towards GSL. However, shallow wells installed in Farmington Bay suggest a combination of atmospheric equilibration while salty (from inundation of GSL at high lake stands) and degassing of old mountain block water (from subsurface salinification). Constraining the age and origin of groundwater discharging into GSL is essential for evaluating the resilience of inflow. We aim to integrate environmental tracer techniques with electrical resistivity tomography, hydraulic head gradients, and other environmental tracers (major ions, salinity, CFC’s, SF6’s, δ¹⁸O, and δ²H) to develop a more robust conceptual framework of groundwater inflow to Great Salt Lake.