SUBSURFACE PERSISTENCE OF CRUDE OIL SPILLED ON LAND AND ITS TRANSPORT IN GROUNDWATER

Abstract

ABSTRACT The persistence of water-soluble hydrocarbons from crude oil spills on land was investigated as a source of groundwater contamination by means of theoretical models, percolation experiments, and the analysis of core samples from spill sites. Examination of a one-dimensional flow model of convection, dispersion, biodegradation, and adsorption of an oil-water solution beneath a water table revealed that under certain conditions adsorption has no effect on the maximum oil concentration reached at any given distance from a spill. Chemical analysis of water percolated through an oil spill zone in a sand trough and also through soil cores taken at spill sites revealed that it may take the equivalent of much more than 100 times the average annual rainfall of Calgary to diminish the water-soluble components in the leachate to a level acceptable in drinking water. Measurements of the amount of alkanes and isoprenoids as functions of depth in field cores at spill sites of various ages and locations indicated that biodegradation rates are much lower in the anaerobic zone than above. Theoretical predictions indicate that contaminated groundwater may 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 oil in the subsoil resulting from spills on land has the potential to pose very long-term threats to groundwater quality and, by the mechanism of resurfacing, to vegetation.