12 - High-Resolution Characterization (Tomographic Surveys)

Summary

ADE with macrodispersion (Fickian) and non-Fickian models rely on the aquifer-scale ensemble mean concept. They satisfy our needs only in the ensemble mean sense, rather than at one field site unless the tracer cloud reaches ergodicity or the tracer plume has experienced enough heterogeneity. The applicability of current theories to an aquifer (one realization of the ensemble) is inadequate at our interest and observation scales. Such scale issues demand a high-resolution delineation of the multi-scale heterogeneity in the aquifer. This chapter introduces new technologies (hydraulic and geophysical tomographic surveys) that minimize reliance on the large-scale ensemble mean models. Most importantly, it demonstrates the effects of interaction between different regional-scale velocities on mixing, dilution, and dispersion---a testimony of the importance of dominant large-scale flow on solute transport. This chapter, in essence, promotes a better understanding of solute migration in field-scale geologic media to minimize our prediction uncertainty.