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Model Report

Exposure Analysis Modeling System

Last Revision Date: 11/16/2009 View as PDF
General Information Back to Top
Model Abbreviated Name:

Model Extended Name:

Exposure Analysis Modeling System
Model Overview/Abstract:
The Exposure Analysis Modeling System (EXAMS) is an interactive software application for formulating aquatic ecosystem models and evaluating the fate, transport, and exposure concentrations of synthetic organic chemicals including 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 user's 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.
Keywords: Pesticide, Compartment Model, Solute Fate and Transport
Model Technical Contact Information:
Dirk F. Young, Ph.D.
Model Coordinator
Environmental Fate and Effects Division (mail code: 7507P)
Office of Pesticides, USEPA
1200 Pennsylvania Ave, NW
Washington, DC 20460-0001
Phone: 703-605-0206
Model Homepage: http://www.epa.gov/ceampubl/swater/exams/index.htm

User Information Back to Top
Technical Requirements
Computer Hardware
Intel-based (or equivalent) PC system
Compatible Operating Systems
Download Information
The model is available gratis from the U.S. EPA.
Using the Model
Basic Model Inputs
Complex model with substantial input requirements including chemical fate parameters, daily weather data, environment characterization.
Basic Model Outputs
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).
Persistence: the time required for natural purification of the ecosystem (via export and degradation processes) once chemical releases end.
User Support
User's Guide Available?
The EXAMS user's guide can be downloaded.

The user's guide includes documentation of the model?s conceptual basis, underlying science, algorithms, model verification studies, data dictionary, and example model development and use sessions.

User Qualifications
Environmental Scientist with knowledge of chemical fate and transport and aquatic systems

Model Science Back to Top
Problem Identification
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.
Summary of Model Structure and Methods
The model uses a modeling framework that links several related models, modules, or sub-models. Equations and algorithms extensively documented in the user guide at (http://www.epa.gov/ceampubl/swater/exams/index.htm). Numerical solutions are employed to solve multi-compartment systems.

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.

Model Evaluation
Substantial regulatory use by EPA Office of Pesticide Programs

Model corroboration studies are either documented or cited in the user guide at (http://www.epa.gov/ceampubl/swater/exams/index.htm)

A problem-specific sensitivity analysis is provided as a standard model output.

Key Limitations to Model Scope
Daily times scale for mass inputs and concentrations. Monthly time scale for variations in environmental parameters (wind, temperature, inflow, etc).
Case Studies
See user manual (http://www.epa.gov/ceampubl/swater/exams/index.htm).

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