The fate of six organic compounds during rapid infiltration of primary wastewater through soil columns was studied. Breakthrough profiles of o-phenylphenol were relatively consistent during the test, with fractional breakthrough (mass output/mass input) being independent of input concentration. Consistent profiles were also observed for 2-(methylthio) benzothiazole, although fractional breakthroughs were higher at lower input concentrations, indicating that removal processes were operating less efficiently at these levels. The behavior of p-dichlorobenzene was similar to that of 2-(methyl-thio)benzothiazole after the first inundation cycle, with the exception that increased fractional breakthroughs were observed at the highest input concentration as well. Microbial adaptation was evident for benzophenone, 2-methylnaphthalene, and p-(1,1,3,3-tetramethylbutyl)phenol, as indicated by increased removal efficiencies during successive inundation cycles, especially at the higher input concentrations. Columns effluent concentrations of the latter two compounds were independent of input concentrations during the final stage of the test. Microbial activity and adaptation were confirmed for several of the compounds by using isotopes and measuring the extent of mineralization in batch tests with soil from one of the columns. The data demonstrate that microbial activity is important in the removal of several trace organic compounds during rapid infiltration of wastewater and that this removal is generally enhanced by the presence of adapted microflora.