Gasoline Residual Saturation in Unsaturated Uniform Aquifer Materials

Approximately 110 billion gallons of gasoline, as a motor fuel, are used in the United States each year. Nearly every gallon is at some time stored underground without environmental regulation. Hundreds of thousands of gasoline leaks to the subsurface may be presently occurring. This paper examines the importance of the residual saturation capacity of a soil to gasoline and proposes a rapid, approximate method for determining the residual saturation capacity of soil to gasoline. Residual saturation capacity was experimentally measured for several soils. Soil particle size, soil density and moisture content were varied in the experiments. Sands at field capacity moisture content had lower residual saturation capacities than dry sands. Empirical relationships were developed which predict specific gasoline retention based upon the volume of sand contacted, sand density, particle diameter and moisture content. Least square linear regression analyses indicate correlation coefficients of 0.98 and 0.94 for the empirical relationships developed for dry sand and sand at field capacity moisture content, respectively. While the sands represent rather ideal soils, the empirical relationships should be useful to those involved in field evaluations of gasoline spills.