Information on the long-term movement of radioactive fission products and other pollutants from waste pits, fallout, and underground nuclear explosions is persued through theoretical and experimental investigations of the various phenomena that pertain to ion transport or retention by soils. The theoretical section explores the interactions between solids in water that result from thermal forces, electrostatic charges, and van der Waals forces. The particle range considered is that of the large colloid to the finest silt. Special attention is given to sources of energy sufficient to cause breakage of adsorption bonds, additive bonding, and the relationship between suspended particles and the granules making up the aquifer. The experimental section explores factors which influence either retention of radioactivity by the sand bed or transport of the activity through such a bed by micro-particles.