File: ABSTRACT.TXT

                            MULTIMED
              Multimedia Exposure Assessment Model
                 Application and Theory Manuals
                          Version 1.01

                          December 1992


         Center for Exposure Assessment Modeling (CEAM)
              U.S. Environmental Protection Agency
               Office of Research and Development
                Environmental Research Laboratory
                    960 College Station Road
                   Athens, Georgia  30605-2720

                          706/546-3549



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Summary

The Multimedia Exposure Assessment Model (MULTIMED) for exposure assessment
simulates the movement of contaminants leaching from a waste disposal
facility.  The model consists of a number of modules which predict
concentrations at a receptor due to transport in the subsurface, surface
water, or air.  The model includes options for directly specifying
infiltration rates to the unsaturated and saturated zones, or a MULTIMED
module can be used to estimate infiltration rates.

When applying MULTIMED to Subtitle D (hazardous waste) facilities, the
landfill, surface water, and air modules in the model are not accessible by
the user; only flow and transport through the unsaturated zone and transport
in the saturated zone can be considered.  MULTIMED uses a steady-state,
one-dimensional, semi-analytical module to simulate flow in the unsaturated
zone. The output from this module, water saturation as a function of depth,
is used as input to the unsaturated zone transport module.  The latter
simulates transient, one-dimensional (vertical) transport in the unsaturated
zone and includes the effects of longitudinal dispersion, linear adsorption,
and first-order decay.  The unsaturated zone transport module calculates
steady-state or transient contaminant concentrations.  Output from both
unsaturated zone modules is used to couple the unsaturated zone transport
module with the steady-state or transient, semi-analytical saturated zone
transport module.  The latter includes one-dimensional uniform flow,
three-dimensional dispersion, linear adsorption, first-order decay, and
dilution due to direct infiltration into the groundwater plume (67,68).

The fate of contaminants in the various media depends on the chemical
properties of the contaminants as well as a number of media- and
environment-specific parameters.  The uncertainty in these parameters can be
quantified in MULTIMED using the Monte Carlo simulation technique.  To
enhance the user-friendly nature of MULTIMED, a preprocessor, PREMED, and a
postprocessor, POSTMED, have been developed.  The preprocessor guides the
user in the creation of a correct Subtitle D input file by restricting
certain options and parameters and by settingappropriate defaults.