Wastewater Recharge and Dispersion in Porous Media

For steady flow between a recharging and a pumping well, in an infinite, confined aquifer of homogeneous, isotropic media, theoretical expressions are developed for the spatial and temporal distributions of a conservative substance, introduced at the recharge well. From these expressions, the relative influences of convection, dispersion, and diffusion on the substance distribution are deduced. To test the analytical results, experimental measurements of the distribution of a dilute salt-water tracer in a sand model are presented. The model tests and field problem show that lateral dispersion has a negligible influence on the substance distribution, and molecular diffusion, while not important in the model tests, may be important in field problems. Longitudinal dispersion is important in determining the shape of the tracer distribution within the aquifer, but it has a significant influence on the concentration in the pumping well only for small times when the concentration, c/c₀ < 0.1.