GEOCHEMICAL EVALUATION OF THE HYDRAULIC CONNECTION BETWEEN SNAKE CREEK AND BIG WASH DRAINAGE BASINS, GREAT BASIN NATIONAL PARK

Great Basin National Park (GBNP) is located in eastern Nevada, in the southern Snake Range. High-altitude areas within GBNP serve as the headwater areas for perennial streams on the flanks of the range and are the primary recharge areas for alluvial aquifers in adjoining basins.

The Snake Creek drainage is the largest and most geologically-complex drainage in the park. Currently, surface-water in upper Snake Creek is diverted around a strongly-losing reach of stream channel through a pipeline adjacent to the stream. At high flows (when pipeline intake capacity is exceeded), surface water in Snake Creek originating above the pipeline intake infiltrates the streambed through permeable carbonate rock. However, neither the direction of subsurface movement nor the terminal discharge area of water lost to the streambed is well understood, though some evidence suggests it may flow south in the subsurface toward neighboring Big Wash drainage.

A suite of geochemical tracers (major ions, trace elements, stable- and radio- isotopes, and dissolved noble gases) were obtained on samples from Snake Creek and Big Wash drainages to investigate hydrologic connections and recharge source locations under the presumption that chemical signatures will evolve in predictable ways along connected groundwater flow paths. The use of multiple environmental tracers is intended to place meaningful constraints on developing conceptual models.

Preliminary results identify distinct recharge locations in the upper watersheds and suggest that a fraction of groundwater in fractured carbonate at the mountain front (1) is recharged at the highest altitudes and (2) is a mixture of waters from multiple recharge locations. Additionally, geochemical signals indicate that groundwater is crossing a large-scale detachment fault that was previously thought to be impermeable to groundwater flow.