We characterized some of the physical, chemical, and microbiological properties of soils that have become severely water-repellent and disaggregated several years or decades following oil contamination. A growing number of patches (usually <2 ha) of disaggregated water-repellent soils have recently been discovered throughout the province of Alberta at 20 to 50-yr-old crude oil spill sites. The disaggregated water-repellent soil is usually confined to a dry and powdery surface layer 10 to 15 cm deep, which no longer smells, feels, or looks like it contains any oil. These soils appear to have permanently lost the ability to support plant growth and recover through natural processes. We analyzed samples of disaggregated water-repellent and adjacent normal soils from three old crude oil spill sites to provide a background set of information about these poorly known soils and assist in the development of hypotheses concerning the development and persistence of soil water repellency and structural degradation. Compared with normal adjacent soils, disaggregated nonwettable soils are characterized by: (1) a strong resistance to wetting, as determined by the molarity of ethanol droplet (MED) test; (2) a smaller population of viable and culturable microorganisms, which contains at least some representatives from nonspore-forming bacterial genera; (3) a high content of mineral N and total C, a comparable pH and ratio of exchangeable cations, but a lower cation exchange capacity; (4) a slightly lower clay content, as determined by the Bouyoucos hydrometer method; (5) a comparable water desorption behaviour following forced saturation with water; (6) dry aggregates of a smaller mean weight diameter (MWD), as determined by dry sieving and scanning electron miscroscopic (SEM) analyses; (7) slightly less pronounced thermal reactions when heated up to 525 °C, as determined by differential thermal analyses (DTA); and (8) a reduced ability to support plant growth. From these observations, we infer that disaggregated water-repellent soils found at old crude oil spill sites do not differ appreciably from normal adjacent soils in terms of their inorganic chemistry. Nonwettable and adjacent wettable soils differ mostly in terms of some physical and biological characteristics, which probably stem from differences in the quality of the organic matter they contain. Key words: Crude oil spills, petroleum hydrocarbons, soil water repellency, soil disaggregation, soil hydrophobicity
