| Description |
A monitoring network in the alpine Brighton Basin was established to examine the relationship between air, ground, and noble gas groundwater recharge temperatures. Maximum noble gas groundwater recharge temperatures from 25 samples collected over 2 years averaged 2.9±1.2 °C, within the experimental error of the mean ground temperature of 2.3 °C , and vary from 0 to 7 °C, also comparable to ground temperature variations. Mean ground temperatures in the upper 1 m of soil over the 2 years were 1 °C cooler than mean air temperatures. This offset is explained by modeling a snow effect on ground temperature. This study indicates that interpretation of groundwater recharge temperatures derived from noble gases should be attentive to the local ground temperature effects in recharge areas. Two-dimensional modeling of fluid flow and heat transport are used to quantify effects of groundwater flow on the subsurface thermal regime and determine the lower limit of recharge rates that will produce an observable perturbation such that groundwater temperatures can be used to constrain them. The greatest temperature perturbations occur in the deepest portion of the recharge area. At recharge rates of 10 mm yr"1 or less, the hydrologic disturbance to the subsurface thermal regime is almost completely dependent on the recharge rate. At recharge rates higher than this, the hydrologic disturbance is dependent on both the recharge rate and permeability. At recharge rates of 50 mm yr"1 and greater, the plume of colder water persists towards the discharge area and could be easily measured and used to constrain recharge rates to the system. The Snake Valley area groundwater system was simulated using a threedimensional model incorporating groundwater flow and heat transport. This study represents one of the first regional modeling efforts to include calibration to groundwater temperatures. The inclusion of temperature observations reduced parameter uncertainties over using just water-level altitude and discharge observations. The distribution of simulated transmissivity includes areas of high transmissivity within and between hydrographic areas. Increased well withdrawals within these areas will likely affect a large portion of the study area, resulting in decreasing groundwater levels and discharge to springs and evapotranspiration. |
