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THE HYDROCARBON SPILL SCREENING MODEL (HSSM), VOLUME 2: THEORETICAL BACKGROUND AND SOURCE CODES
Charbeneau, R. J., J W. Weaver*, AND B. K. Lien*. THE HYDROCARBON SPILL SCREENING MODEL (HSSM), VOLUME 2: THEORETICAL BACKGROUND AND SOURCE CODES. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/R-94/039b (NTIS 95-210084), 1994.
A screening model for subsurface release of a nonaqueous phase liquid which is less dense than water (LNAPL) is presented. The model conceptualizes the release as consisting of 1) vertical transport from near the surface to the capillary fringe, 2) radial spreading of an LNAPL lens through the capillary fringe and dissolution of LNAPL constituents into a water table aquifer, and 3) transport in the flowing ground water to a potential exposure location. Each component of the conceptual model is treated as a distinct process by separate models. This report describes the modules for the vadose zone, lateral spreading at the water table and dissolution of constituents into the aquifer, and aquifer transport of the dissolved constituents to receptor points. Spreading of the hydrocarbon lens and dissolution of hydrocarbon constituents are transient phenomena, and the aquifer transport model must be capable of addressing a time variable source term. This is incorporated through application of Duhamel's principle to a gaussian-source plume model. The resulting screening model is computationally efficient and has only moderate parameterization requirements.