TYPE CURVES TO DETERMINE THE RELATIVE IMPORTANCE OF ADVECTION AND DISPERSION FOR SOLUTE AND VAPOR TRANSPORT

The relative importance of advection and dispersion for both solute an d vapor transport can be determined from type curves for concentration , flux, or cumulative nux, The dimensionless form of the type curves p rovides a means to directly evaluate the importance of mass transport by advection relative to that of mass transport by diffusion and dispe rsion. Type curves based on an analytical solution to the advection-di spersion equation are plotted in terms of dimensionless time and Pecle t number. Flux and cumulative flux type curves provide additional rati onale for transport regime determination in addition to the traditiona l concentration type curves. The extension of type curves to include v apor transport with phase partitioning in the unsaturated zone is a ne w development, Type curves for negative Peclet numbers also are presen ted. A negative Peclet number characterizes a problem in which the dir ection of now is toward the contamination source, and thereby diffusio n and advection can act in opposite directions. Examples are the diffu sion of solutes away from the downgradient edge of a pump-and-treat ca pture zone, the upward diffusion of vapors through the unsaturated zon e with recharge, and the diffusion of solutes through a low hydraulic conductivity cutoff wall with an inward advective gradient.