ABSTRACT
This chapter presents a discussion of relationships that govern migration in the subsurface, including the flux equation, Darcy’s Law, and behavioral aspects of gases and vapors. The occurrence and migration of water within the saturated system, including types of aquifers and flow under steady-state and nonsteady-state flow; unsaturated systems and capillary barriers, and groundwater chemistry and quality are subsequently discussed. The average macroscopic flow velocity of a fluid is the average of all the microscopic flow velocities, and is usually observed by tracking some chemical tracer or fluid flow front through the material and is a bulk property of the media. There are several bulk properties of the media that are important and that are more readily determined than their microscopic components. Fick’s Law relates mainly to diffusion of dissolved chemicals with respect to differences in concentration gradients in the material or fluid, or migration of gases or vapors in response to differences in gas pressure.
