1. General Model Information

Name: Hydrocarbon Spill Screening Model

Acronym: HSSM

Main medium: terrestrial
Main subject: hydrology, (eco)toxicology
Organization level: ecosystem
Type of model: partial differential equations
Main application:
Keywords: nonaqueous phase liquid, LNAPL, aquifer contamination, spill, soil, water, vadose zone, hydrocarbon,subsurface flow,benzene, toluene, ethylbenzene, xylenes, methyl tert-butyl ether,leaking, underground storage tank, semi-analytical solution


Center for Exposure Assessment Modeling (CEAM)
National Exposure Research Laboratory - Ecosystems Research Division
Office of Research and Development (ORD)
U.S. Environmental Protection Agency (U.S. EPA)
960 College Station Road
Athens, Georgia (GA)
Phone: 706/355-8400
Fax: 706/355-8302
email: ceam@epamail.epa.gov



The Hydrocarbon Spill Screening Model (HSSM) simulates the subsurface flow of a lighter-than-water, nonaqueous phase liquid (LNAPL) and its associated aquifer contamination. The most common example is a petroleum fuel such as gasoline or diesel that has been released from a leaking underground storage tank. When the fuel reaches the water table, it may form a lens or smear zone. Through the fuel's contact with the aquifer, ground water contamination can result. Chemical components of the fuel (benzene, toluene, ethylbenzene, xylenes, methyl tert-butyl ether) dissolve into the ground water according to their solubilities and the hydrology of the system. The contaminants then can be transported in the aquifer to receptor wells.
One of the most important reasons for inclusion of the LNAPL or fuel phase in simulating aquifer contamination is that the chemical contaminants are released slowly from the fuel phase. Accurate estimation of the loading to the aquifer requires the simulation of contaminant dissolution from the fuel.

HSSM simulates contamination associated with these fuels by using three simplified modules that represent the vadose zone, the fuel lens within the capillary fringe, and the aquifer. Each module was developed from a semi-analytical solution of the governing equations. The simplified solutions reduce the extensive computational burden of a fully numeric approach. Lack of availability of field data often limits usage of complex models, and HSSM attempts to include the important phenomena at a reasonable data and computational cost.

The three modules of HSSM are linked in a windows interface that allows for interactive input of data, running of the models, and automated graphing of the model output. A two volume user's guide provides specific instruction for running the model, guidance on selecting input parameter values and interpreting the model output, in addition to the theoretical background of the model. Example applications to field data problems are available from Internet links given on the HSSM distribution page.

The model conceptualizes the release as consisting of
1) vertical transport from near the surface of the capillary fring,
2) radial spreading of an LNAPL lens through the capillary fring and dissolution of LNAPL constituents into a water table aquifer, and
3) transport in the flowing ground water to a potential exposure lication.
Each component of the conceptual model is treated as a distinct process by separate models. This report describes the modules for the vados 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 adressing 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. Both DOS and Windows interfaces are provided to create input dada sets, run the model, and graph the results. These interfaces simplify the procedures for running the model so that the model user may focus on analysis of his/her problem of interest. To that end, guidance is given for selecting parameter values and several utility programs are provided to calculate certain parameters. Typical example problems, which begin with a general problem statement, show exactly how each parameter of the model should be chosen.

The HSSM model system and its documentation are available for microcomputer (Windows) systems.

Source of abstact: "ftp://ftp.epa.gov/epa_ceam/wwwhtml/hssm.htm" HSSM homepage (not available) at EPA-CEAM (10/99).
see now: HSSM model

II. Technical Information

II.1 Executables:

Operating System(s):
HSSM – Windows

II.2 Source-code:

Programming Language(s): see above

II.3 Manuals:

HSSM – Windows

II.4 Data:

III. Mathematical Information

III.1 Mathematics

III.2 Quantities

III.2.1 Input

III.2.2 Output

IV. References

V. Further information in the World-Wide-Web

HSSM Home-Page at the EPA

VI. Additional remarks

Last review of this document by:
Status of the document:
last modified by J. Benz Wed Sep 26 12:12:44 CEST 2013

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