Transport and biodegradation of NAPLs at subsurface sand/clay interfaces

Throughout the United States, petroleum hydrocarbon contamination of soil is a severe problem. Storage tanks are quite often the source, whereby hydrocarbons are released on or near the ground surface and are free to migrate through the soil to the groundwater. Sometimes, such chemicals accumulate at interface of different soil types. Hexadecane transport and degradation in soil reactors were studied in a series of experiments. Three reactors, consisting of soil in sand-clay-sand layers, were contaminated at single points in the center of the top sand layer just below the surface. One reactor was used as a control while the other two were equipped with influent and effluent water ports located above the sand/clay interface. The ports were utilized to add water to the soil. One reactor was supplied with water only and the other was injected with a phosphorus/nitrogen solution to enhance degradation. The project focused on two aspects: (1) the transport of the NAPLs at an abrupt sand/clay interface and (2) the ability of the soil microbes to degrade the hexadecane under aerobic conditions. Gas chromatography analysis of the effluent water samples indicate no significant removal of the NAPL from the soil by pumping, while mass balances indicate NAPL degradation due to microbial action. In addition, gas chromatography data of soil samples trace the movement of the chemical throughout the three reactors