Hydrogeochemical and environmental isotope investigation of groundwater recharge mechanisms in the Virginia City Highlands, Nevada

Abstract

Stable isotope data and conventional hydrologic data indicate groundwater recharge occurs primarily through stream channels and areas of little soil cover overlying fractured bedrock between the months of October to March. Most light summer storms do not contribute to the area's recharge. Tritium, geochemical data, and stable isotope of soil and groundwaters indicate poor groundwater mixing and relatively little recharge. Slope of 2.5 for the groundwater stable isotope line (GWL) indicates relatively fast non-equilibrium fractionation. Locations of groundwaters along the GWL reflect relative amounts of evaporation prior to recharge; end members of the GWL indicate specific recharge mechanisms. Large coniferous mesophytes are used as lysimeters for sampling the long term stable isotope composition of soil waters. Non-equilibrium fractionation components are established from the GWL. Estimates of fractionation factors based on free Pinion pine xylem and needle waters provide a cross check for using mean temperature fractionation factor values.