In assessing the possible removal of contaminants from soils or sediments by surfactant solutions, the need also arises to elucidate interactions between the surfactants and the components of soils and sediments. Interactions of the anionic surfactant dodecylsulfate (DS) with soil and sediment (medium) components were examined at DS concentrations in the range of the critical micelle concentration (cmc). Experiments involving either the variation in DS (0.1-40 mM) or in medium concentration (0.04-0.36 g/mL for six media) demonstrate the importance of precipitation, micellization, and micellar counterion binding in determining the recovery of aqueous DS from medium slurries. Mechanistic and semiempirical mass action equations, and their associated constants, describing these phenomena in well-defined solutions, along with the necessary material balance equations, permit the calculation of precipitation boundaries. Calculated precipitation boundaries were compared to experimental results. These equations also allow the calculation of the aqueous micelle and monomer DS concentrations. A similar methodology to calculate the aqueous micelle concentration was applied in the subsequent study to quantitatively assess the distribution of PAH compounds among micellar, medium, and dissolved aqueous phases.