RESIDUAL GASOLINE SATURATION IN UNSATURATED SOIL WITH AND WITHOUT ORGANIC-MATTER

The goal of this study was to investigate the influence of one variabl e, natural organic matter, on residual gasoline saturation in sandy so ils. Capillary pressure-saturation (P-c-S) relationships (air-gasoline ) were determined for three physically-similar sandy soils, with diffe rent organic carbon contents (0.086%, 0.89% and 1.65%) and residual ga soline saturations were compared. Two initial moisture conditions, res idual water saturation and air-dry, were evaluated. One soil type was packed to two different bulk densities. Visualization of the soils usi ng cryo-scanning electron microscopy was performed to aid in better un derstanding the role of the organic matter in the soil. The results sh owed that soils with higher organic contents had higher residual gasol ine saturations when starting with an initially air-dry soil. Increasi ng the bulk density of the same air-dried soil resulted in an increase in residual gasoline saturation. In the presence of a residual water saturation, however, residual gasoline saturations were virtually iden tical for the three soils and independent of bulk density; approximate ly 5-10 times lower than in soil that was initially air-dry. The prese nce of the residual water effectively coated the surface of the soil t hereby reducing or eliminating gasoline/soil interactions. Some residu al water may also be occupying very small pore spaces, making these lo cations inaccessible to the gasoline. (C) 1997 Elsevier Science B.V.