An integrated approach for estimating oil volume in petroleum-contaminated sites - a North American case study

Subsurface contamination by light nonaqueous phase liquids (LNAPLs) such as hydrocarbon spill and leakage is a serious problem in North America. Following release of hydrocarbons in the subsurface, significant amounts of the fluid are trapped in soil by capillary forces and in saturated zone due to slow groundwater flow. Removal of these trapped free phase LNAPLs is critical because it will not only provide the possibility for complete cleaning up but also prevent further contamination and thus potential environment/public health risks. Estimation for volume of these trapped free LNAPLs is the first step before any further studies or actions can be undertaken. In this study, an integrated approach is employed for estimating LNAPLs distribution in porous media at a site located in western Canada. The site has one original release source that is a flare pit. Spilled petroleum products in past two decades seriously contaminated the on-site soil and groundwater. More than ten monitoring wells are located around the emission sources. At most of them, free phase LNAPLs have been found since early 1980s. Result of this case study reveals that soil properties and site heterogeneous characteristics have significant impacts on the spreading of contaminants and thus oil volume estimation. The LNAPLs in subsurface do not simply present themselves as a distinct layer floating over a capillary fringe. In general, this proposed method could serve as an effective and convenient tool for obtaining reasonable estimation of residual oil volume in subsurface. The results offer insight into the contamination details and are useful for further modeling and remediation studies.