USING NATURAL TRACERS TO TEST NUMERICAL GROUND-WATER MODEL RESULTS

Confirming ground-water modeling simulations is often difficult because adequate hydraulic data such as head and flux measurements are unavailable or predicted model results might not occur for years. However, natural tracers, such as stable isotopes, ground-water temperature, electrical conductivity, pH, and major ions, can be used as an independent measurement of some modeling results. This can help constrain the range of conceptual models and associated model predictions.

We present the results of monitoring natural tracers at several sites in a range of hydrogeological settings to show how natural tracers can help test the results of numerical modeling. In Door County, Wisconsin, short-term fluctuations of ground-water temperature and electrical conductivity agree with particle-tracking results from a numerical model to indicate that recharge water travels through a fractured dolostone aquifer at high velocities. In Clinton, New York, rapid changes in temperature, conductivity, and major ion concentrations suggest that municipal production wells in an unconfined aquifer are affected by surface water consistent with model simulations. In La Crosse, Wisconsin, oxygen isotope and temperature breakthrough data show that surface water moves into an alluvial aquifer at rates predicted by a numerical model.