Investigation into mechanisms leading to the development, spread and persistence of soil water repellency following contamination by crude oil

We investigated mechanisms by which soil water repellency may develop, spre ad and persist at old crude oil spill sites. We tested if its development m ay be due to soil sorption of vapour-phase petroleum compounds, its spread due to mechanical dispersal and mixing, and its persistence due to associat ion of causative agents with humin and soil mineral surfaces. Development. Readily wettable soils acquired water repellency following 60 d of storage in the presence of oil-contaminated subsoil material. Change in soil wettab ility was attributed to soil sorption of vapour-phase petroleum compounds e manating from the contaminated material. We cite literature reports indicat ing that liquid-phase petroleum compounds can also cause soil water repelle ncy. To that effect, we report how we tested and finally rejected the hypot hesis that sorption of petroleum asphaltenes might be the sole cause of soi l water repellency. Spread. We describe how mixing one mass unit of water-r epellent soil with two to four mass units of wettable adjacent soil is suff icient to impart severe water repellency to soil mixes from three sites. Pe rsistence. The water-repellent condition found at old crude oil spill sites is highly resistant to natural weathering and nondestructive extraction pr ocedures. We show here that it also resists exhaustive extraction with 0.1 M NaOH and conclude that causative agents of soil water repellency are at l east not solely associated with humic and fulvic acid fractions.