The Hydrocarbon Spill Screening Model (HSSM) is intended for simulation of subsurface releases of light nonaqueous phase liquids (LNAPLs) in homogeneous soils. The model consists of separate modules for LNAPL flow through the vadose zone, spreading in the capillary fringe, and dissolved transport of chemical constituents of the LNAPL in a water table aquifer. These modules are based on simplified conceptualizations of the flow and transport phenomena which were used so that the resulting model would be a practical, though approximate tool.

Spreading in the capillary fringe is assumed radial and not subject to a regional gradient of the water table. Advective-dispersive transport of dissolved phase in the saturated zone is subject to regional uniform flow and recharge. The source is assumed at the soil surface and may be a constant flux source, a volume source, or a constant head source. The modules KOPT and OILENS provide a time-variable source condition for the aquifer transport model. Graphic output includes saturation profiles, NAPL lens contaminant mass balance, and receptor concentration histories. HSSM includes a soil property regression utility to estimate soil hydraulic properties using the regression equations of Rawls and Brakensiek (1985). It also includes a utility for calculation of the NAPL/water partition coefficient based on Raoults law.

Both DOS and Windows interfaces are provided to create input data sets, run the model, and graph the results. Guidance is given for selecting parameter values and several utility programs are provided to calculate parameters. Typical example problems, which begin with a general problem statement, show how each parameter of the model should be chosen.

SYSTEM REQUIREMENTS

DOS Version: Intel 8086 or higher microprocessor, at least 400 Kb free (low) RAM, DOS 3.1 or higher, hard disk with at least 2 Mb free disk space, EGA/VGA graphics; the program will run as a DOS application under MS Windows.

MS-Windows version: Intel 8086 or higher microprocessor, at least 640 Kb (low) RAM (preferably 1 Mb RAM to run MS Windows in enhanced mode), DOS 5.1 or higher, hard disk with at least 2 Mb free disk space, EGA/VGA graphics, MS Windows 3.0 or later, and Microsoft compatible mouse.

Developers: J.W. Weaver, and B.K. Lien (EPA R.S. Kerr Env. Res. Lab.), R.J.J. Charbeneau (University of Texas at Austin), and J.B. Provost (Computer Sciences Corporation)