A multiple-tracer approach to understanding regional groundwaterflow in the Snake Valley area of the eastern Great Basin, USA

Groundwater in Snake Valley and surrounding basins in the eastern Great Basin province of the western
United States is being targeted for large-scale groundwater extraction and export. Concern about declining
groundwater levels and spring flows in western Utah as a result of the proposed groundwater withdrawals
has led to efforts that have improved the understanding of this regional groundwater flow system. In this
study, environmental tracers (del2H, del18O, 3H, 14C, 3He, 4He, 20Ne, 40Ar, 84Kr, and 129Xe) and major ions from
142 sites were evaluated to investigate groundwater recharge and flow-path characteristics. With few
exceptions, del2H and del18O show that most valley groundwater has similar ratios to mountain springs,
indicating recharge is dominated by relatively high-altitude precipitation. The spatial distribution of 3H,
terrigenic helium (4Heterr), and 3H/3He ages shows that modern groundwater (<60 yr) in valley aquifers
is found only in the western third of the study area. Pleistocene and late-Holocene groundwater is found
in the eastern parts of the study area. The age of Pleistocene groundwater is supported by minimum
adjusted radiocarbon ages of up to 32 ka. Noble gas recharge temperatures (NGTs) are generally
1–11 degrees C in Snake and southern Spring Valleys and >11 degrees C to the east of Snake Valley and indicate a
hydraulic discontinuity between Snake and Tule Valleys across the northern Confusion Range. The
combination of NGTs and 4Heterr shows that the majority of Snake Valley groundwater discharges as
springs, evapotranspiration, and well withdrawals within Snake Valley rather than continuing
northeastward to discharge at either Fish Springs or the Great Salt Lake Playa. The refined understanding
of groundwater recharge and flow paths acquired from this multi-tracer investigation has broad
implications for interbasin subsurface flow estimates and future groundwater development.