[en] This paper reports on petroleum-derived hydrocarbons and chlorinated solvents that are the most common organic contaminants of ground waters, including those used as drinking-water supplies. Leaks and spills of storage tanks and associated piping plus inappropriate disposal methods in pits and landfills are common sources of these pollutants. The behavior of 1,1,1-trichlorethane, trichlorethylene, benzene, toluene, chlorbenzene, n-xylene, and o-xylene was studied in material from an aviation gasoline spill site. The plume of contamination has been extensively characterized hydrologically and geochemically and will be discussed in conjunction with the laboratory data. Laboratory studies were initiated to confirm field evidence of biological transformation of alkylbenzenes. The material chosen for study was obtained from an adjacent pristine area and from both oxic and anoxic zones of biological activity in the plume. Preliminary results indicate the degradation of benzene, toluene m-xylene, o-xylene, and chlorobenzene. No degradation of 1,1,1-trichlorethane or trichlorethylene has been observed