Quantifying stream-loss recovery in a spring using dual-tracer injections in the Snake Creek drainage, Great Basin National Park, Nevada, USA

Simultaneous short-pulse injections of two tracers (sodium bromide [Br – ] and fluorescein dye) were made in a losing reach of Snake Creek in Great Basin National Park, Nevada, USA, to evaluate the quantity of stream loss through permeable carbonates that resurfaces at a spring approximately 10 km down drainage. A revised hydrogeologic cross section for a possible flow path of the infiltrated Snake Creek water is presented, and the results may inform water management in the region. First arrival and peak concentration of the two tracers occurred at 9.5 and 12.7 days after injection, respectively. Fracture transport simulations indicate that Br – preferentially diffuses into immobile regions of the aquifer, and this diffusive flux is likely responsible for the major differences in the breakthrough curves. When considering the diffusive tracer flux, total apparent Br – and fluorescein dye recoveries were 16.9–22.1% and 21.7–24.3%, respectively. These findings imply that consideration of diffusive flux and long-term monitoring in fracture-dominated flow may support accurate quantification of tracer recovery. In addition, the apparent power law slopes of the breakthrough tails for both tracers were steeper at early times than have been attributed to heterogeneous advection or channeling in meter-scale tests, but the late-time Br – power law slope becomes less steep than has been attributed to diffusive exchange. These deviations may reflect fracture transport patterns that occur at larger scales. Des injections simultanées de courte impulsion, de deux traceurs (bromure de sodium [Br – ] et fluorescéine) ont été réalisées dans le bief de la perte du Snake Creek dans le Parc National du Grand Bassin, Nevada, Etats-Unis d’Amérique, afin d’évaluer le volume de la perte à la traversée des formations carbonatées perméables qui affleurent au droit d’une source située à environ 10 km à l’aval du bassin. Une coupe transversale hydrogéologique révisée montrant un cheminement d’écoulement possible de l’eau du Snake Creek infiltrée est présentée, et ces résultats peuvent éclairer la gestion de l’eau dans la région. La première arrivée de la restitution et le pic de concentration des deux traceurs se sont produits respectivement 9.5 et 12.7 jours après l’injection. Les simulations du transport dans la fracture indiquent que le Br – diffuse préférentiellement dans les secteurs immobiles de l’aquifère et que ce flux diffusif est probablement à l’origine des différences majeu