PERFORMANCE AND ANALYSIS OF AQUIFER TRACER TESTS WITH IMPLICATIONS FOR CONTAMINANT TRANSPORT MODELING-A PROJECT SUMMARY

ABSTRACT The scale‐dependence of dispersivity values used in contaminant transport models to estimate the spreading of contaminant plumes by hydrodynamic dispersion processes was investigated and found to be an artifact of conventional modeling approaches (especially, vertically averaged parameters in two‐dimensional plume simulations). The work reported here shows that variations in hydraulic conductivity with depth result in significant variations in ground‐water flow and contaminant transport velocities; it is the resulting velocity variations that, if vertically averaged, give rise to apparent scale‐dependency of dispersion (e.g., increased dispersion with increasing travel distance). Special depth‐selective observation well designs are recommended by the authors for use in tracer tests, so that detailed estimates of the variations in hydraulic conductivity, and flow and transport velocities can be obtained. Innovative modeling techniques that take advantage of the detailed information obtainable from such tests (by emphasizing advective transport, as opposed to dispersive transport), have been developed by the authors. These modeling techniques are shown to have an element of true predictive ability, being able to closely simulate actual results with little or no calibration.