Oil spills on land as potential sources of groundwater contamination

Abstract

A detailed study was made of the subsurface persistence of oil spilled on land and its potential as a source of groundwater contamination. Theoretical models, laboratory experiments and analysis of core samples from a number of spill sites were used in the study. A one-dimensional flow model of convection, dispersion, biodegradation, and sorption of an oil-water solution revealed that under certain conditions sorption has no effect on the maximum oil concentration reached at any given distance from a spill. Chemical analysis of water percolated through oil-contaminated soil samples prepared in the laboratory and also through soil cores taken at various spill sites revealed that it would take the equivalent of over 100 times an average annual rainfall of 46 cm to reduce the water-soluble components in the leachate to a level acceptable in drinking water. Analysis of core samples from spill sites of various ages and locations indicated that biodegradation of oil is extremely slow in the anaerobic zone of the soil. Theoretical predictions indicated that contaminated groundwater might extend in the direction of flow from less than one meter to several thousand meters from a spill, depending primarily on biodegradation rates and pore velocities. It is concluded that some oil spills on land have the potential to pose long term threats to groundwater quality. For a given oil spill site, the extent of long-term groundwater contamination can be predicted easily by simple laboratory measurements and transport models developed in this study.