CONSTRAINTS ON RECHARGE TO THE ESPAÑOLA BASIN PROVIDED BY A NUMERICAL FLOW MODEL CALIBRATED WITH GROUND-WATER AGE, TEMPERATURE, AND RECHARGE TEMPERATURE DATA

Like most intermountain basins in the western United States, recharge to the Española Basin in northern New Mexico is uncertain. Ground-water age, temperature, and noble gas recharge temperature data were collected from throughout the basin to improve constraints on recharge rates and locations, particularly the component of recharge that infiltrates in surrounding mountains (mountain-block recharge, or MBR). Carbon-14 ages were modeled for the basin well samples using NETPATH. Temperature profiles were measured in wells up to 670m deep. Recharge temperatures were modeled from dissolved noble gas concentrations, then used to limit possible recharge elevations for basin well waters by employing a local recharge temperature versus elevation relationship. The tracer data alone reveal important aspects of the flow system; e.g., recharge temperatures of waters with modeled ages <10,000 years confirm that MBR is a significant recharge component (>30%) on the eastern side of the basin. However, to fully evaluate the utility of these environmental tracers in characterizing intermountain flow systems, tracer results are being used to re-calibrate an existing 3-D, finite element, ground-water flow model of the basin, adding in heat transport. Calibration is being performed using an automated inverse approach (PEST), which allows for the quantification of uncertainty in modeled parameters. Results will be presented indicating the degree to which uncertainties in modeled recharge rates and locations are reduced by calibrating to age, temperature, and recharge temperature in addition to conventional hydraulic measurements (hydraulic head and discharge rate).