Salt Crust, Brine, and Marginal Groundwater of Great Salt Lake's North Arm (2019 To 2021)

Following the construction of the railroad causeway in 1959, a perennial halite (NaCl) bottom crust has been known to exist in the north arm (Gunnison Bay) of Great Salt Lake, Utah, but the lake conditions controlling accumulation or dissolution of the crust are not well defined, including how depth-controlled chemodynamic and hydrodynamic factors influence the degree of the halite saturation. Immediately prior to the opening of a new bridge in the causeway in early December 2016 when north arm lake elevation was at a historical low (just above 4189 feet), the north arm lake brine was at halite saturation. After the opening, inflow of less saline south arm water mixed with north arm water, raised lake elevation, and diluted the north arm lake brine to undersaturation with respect to halite. The following five years have resulted in annual and seasonal fluctuations of halite saturation states. Beginning in mid-2019, the Utah Geological Survey began a study of the north arm to better understand and document the transitions of halite saturation state following the bridge opening using newly collected data as well as reviewing available past data.