Reduction of subsurface movement of liquids was the subject of a 1-day symposium sponsored by Committee D-18 on Soil and Rock of the American Society for Testing and Materials (ASTM) and cosponsored by the U.S. Committee on Large Dams (USCOLD) of the International Commission on Large Dams. The Symposium on Impermeable Barriers for Soil and Rock, the first specialized symposium of its kind, was held in Denver, Colorado, on June 25, 1984. The program emphasized the interaction of the environmental system of soil and rock containment, impermeable barriers, and enclosed liquids. The theory, testing, and design considerations of such interactive systems was explored in relation to slurry walls and clay and earth additive linings as applied to geotechnical engineering projects such as tailings and waste containment ponds, landfills, solar and biomass ponds, ditches, canals, and reservoirs. A number of papers presented research results on the interaction of various chemical and hazardous wastes with the soil and rock materials and lining or slurry materials.