Hydrocarbon Fate and Transport Predictions: When are One-Dimensional Solute Transport Calcuilations Valid?

G. D. Beckett, David Huntley, and M. P. Wiedlin

Some petroleum contaminated sites do not pose adverse human or environmental risk. Hydrocarbon fate and transport calculations are often used to estimate potential concentrations reaching sensitive receptors to then determine risk. Many regulatory organizations suggest the use of 1-dimensional solute controlled models (e.g., SESOIL, VLEACH) to determine hydrocarbon fate and transport. These simple models assume that the geologic environment is 1-dimensional and that contaminants travel as dissolved solutes with an associated vapor-phase. However, the actual release consists of hydrocarbon non-aqueous phase liquid (NAPL) in a 3-dimensional environment, with subsequent transport in dissolved and vapor phases. Therefore, a priori assumptions in the use of 1-dimensio al solute controlled models are that the NAPL phase is immobile and the multidimensional characteristics of a site are irrelevant. These models also assume simplified mechanisms of unsaturated flow that also affect predicted outcomes.

Because actual releases are not represented by 1-dimensional solute transport, it is useful to characterize the uncertainty in the resultant predictions. This paper compares 1-dimensional solute transport predictions to 2-dimensional multiphase cross-section predictions under three different release scenarios and quantifies differences in outcomes.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California