                                                           File: ABSTRACT.TXT


                        EXAMS Model System Abstract


               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 30605-2700

                                706/355-8400



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                                  Summary

The Exposure Analysis Modeling System, first published in 1982
(EPA-600/3-82-023), provides interactive computer software for formulating
aquatic ecosystem models and rapidly evaluating the fate, transport, and
exposure concentrations of synthetic organic chemicals - pesticides,
industrial materials, and leachates from disposal sites.  EXAMS contains an
integrated Database Management System (DBMS) specifically designed for
storage and management of project databases required by the software.  User
interaction is provided by a full-featured Command Line Interface (CLI),
context-sensitive help menus, an on-line data dictionary and CLI users'
guide, and plotting capabilities for review of output data.  EXAMS provides
20 output tables that document the input data sets and provide integrated
results summaries for aid in ecological risk assessments.

EXAMS' core is a set of process modules that link fundamental chemical
properties to the limnological parameters that control the kinetics of fate
and transport in aquatic systems.  The chemical properties are measurable by
conventional laboratory methods; most are required under various regulatory
authorities.  EXAMS limnological data are composed of elements historically
of interest to aquatic scientists world-wide, so generation of suitable
environmental data sets can generally be accomplished with minimal project-
specific field investigations.

EXAMS provides facilities for long-term (steady-state) analysis of chronic
chemical discharges, initial-value approaches for study of short-term
chemical releases, and full kinetic simulations that allow for monthly
variation in mean climatological parameters and alteration of chemical
loadings on daily time scales.  EXAMS has been written in generalized
(N-dimensional) form in its implementation of algorithms for representing
spatial detail and chemical degradation pathways. The complexity of the
environmental description and the number of chemicals is fully user-controlled.
This implementation allows for direct access file (UDB) storage of five
interacting chemical compounds and 100 environmental segments; more complex
configurations can be created and subsequently stored using EXAMS' write
command.  EXAMS provides analyses of

     Exposure: the expected (96-hour acute, 21-day and long-term chronic)
     environmental concentrations of synthetic chemicals and their
     transformation products,

     Fate: the spatial distribution of chemicals in the aquatic ecosystem,
     and the relative importance of each transformation and transport process
     (important in establishing the acceptable uncertainty in chemical
     laboratory data), and

     Persistence: the time required for natural purification of the ecosystem
     (via export and degradation processes) once chemical releases end.

EXAMS includes file-transfer interfaces to the PRZM3 terrestrial model and
the FGETS and BASS bio-accumulation models; it is a complete implementation
of EXAMS in Fortran 95.

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