An index for ranking the mobility of organic compounds in soil systems is presented. The index is defined as the ratio of time required for an organic constituent to travel through a given depth of soil (e.g., soil treatment zone), and the constituent half‐life due to degradation assuming a first‐order degradation rate. The mobility and degradation index (MDI) has been evaluated as a function of the constituent retardation factor in soil and degradation half‐life for several soil textures. This approach is useful for the design and management of hazardous waste land treatment systems, as well as for treatment of previously contaminated soil.