ABSTRACT
In field situations where there are very low hydraulic conductivities or very small hydraulic gradients, there will be little or no fluid flow. In these cases, the mass flux through a barrier may be controlled by chemical concentration gradients. This phenomenon was discussed in Chapter 1. Since clay minerals are surrounded by adsorbed cations in amounts of 5-150 milliequivalents/ 100 g of solid, the replacement of exchange cations and, in some cases, anions, becomes an important factor in retardation of certain dissolved species. Therefore, retardation and the use of distribution coefficients is also discussed.
