ABSTRACTTo help demonstrate the ability to operate a hazardous waste landfill with no escape of leachate, permeameter tests of the effects on clay liner material of leachates containing ppm levels of organics such as chloroform, methylene chloride, toluene, and chlorobenzene were run. To get an unambiguous future determination of a detection of failure by leachate leakage into the landfill underliner monitoring system, a single compound or agent was sought which could be used as a tracer material. Fluorobenzene was chosen because of its physicochemical properties and its uniqueness in the normal industrial waste stream.The leachate permeameter testing confirmed literature data indicating that dilute concentrations of organic solvents in landfill leachate do not impair the barrier properties of clay even after several pore volumes of throughput.The appropriateness of the choice of fluorobenzene was confirmed by examining its comparative migration and by looking for its effects on the clay. Modeling of permeameter solute effluent concentration data with the transport equation of Ogata (1970) has shown a reasonable fit. Retardations of the major components of the particular landfill leachate evaluated were as expected, with chlorobenzene>toluene>fluorobenzene = chloroform>methylene chloride. Fluorobenzene is a good representative of the least retarded chemicals. There were no adverse effects on the clay's barrier properties from the ppm level of fluorobenzene added to the leachate.