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The Hydrocarbon Spill Screening Model (HSSM)
The Hydrocarbon Spill Screening Model (HSSM) was developed by theU. S. Environmental Protection Agency to serve as a simplified model for subsurface releases of fuel hydrocarbons. The most common problem that the model may be used to address is that of a leaking underground storage tank. As of the end of 1997, there have been over 400,000 confirmed releases from underground storage tanks in the U.S.
For subsurface contamination, the most important characteristics of fuel hydrocarbons are that they are:
- immiscible with water (oil and water don't mix)
- less dense than water
- composed of chemicals that have varying water solubilities and volatilities
- composed of a number of chemicals that can have adverse health affects
These features are built into the model so that the model:
- tracks the flow of the water-immiscible fuel
- simulates the dissolution of various chemicals (benzene, toluene, ethylbenzene, xylenes or MTBE) into ground water
- transport of contaminants to receptors in aquifers
Why is it important to include these characteristics and features in the model?
Modeling aquifer contamination requires some treatment of the release of contaminants into the aquifer. Since the source of contaminants for these problems is a fuel phase, release of BTEX or MTBE from the fuel phase drives the creation and persistence of the contaminant plume in the aquifer. This is one of the major components of mass
balance for contaminant plumes (the others being--transport in the aquifer and losses due to biodegradation and other processes) Because HSSM includes the fuel as a separate phase it can simulate the release of contaminants to the aquifer. Without this component (i.e., models that only include aqueous contaminants) arbitrary assumptions must be made concerning the source of the contaminants.
Additional EPA Modeling Resources
For further information on the Hydrocarbon Spill Screening Model contact:
Dr. Jim Weaver (firstname.lastname@example.org)
Ecosystems Research Division
National Exposure Research Laboratory
United States Environmental Protection Agency
960 College Station Road
Athens, Georgia 30605-2700
+1 706 355 8329