ABSTRACT
This chapter presents a variety of laboratory and field experimental techniques that lend credibility to the observation of physical nonequilibrium processes in heterogeneous soil systems. A relatively simple technique for confirming and quantifying physical nonequilibrium in soil systems involves displacement experiments performed at a variety of experimental fluxes using a single representative tracer. In homogeneous systems, such as a well-packed bed of silica sand, where pore size heterogeneities are limited, physical nonequilibrium may still control the rate of solute interaction with the solid phase. Quantifying physical nonequilibrium processes at the field scale using variations in pore-water flux are rare due to the difficulty of providing enough water to drive solute mobility within the system. In the laboratory, pressureheads are imposed upon soil samples or columns so that pore class sets can be either included in, or excluded from the tracer displacement experiment.
