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Model Report


Last Revision Date: 12/09/2009 View as PDF
General Information Back to Top
Model Abbreviated Name:

Model Extended Name:

Model Overview/Abstract:
MINTEQA2 is a equilibrium speciation model that can be used to calculate the equilibrium composition of dilute aqueous solutions in the laboratory or in natural aqueous systems. The model is useful for calculating the equilibrium mass distribution among dissolved species, adsorbed species, and multiple solid phases under a variety of conditions including a gas phase with constant partial pressures. A comprehensive data base is included that is adequate for solving a broad range of problems without need for additional user-supplied equilibrium constants. The model employs a pre-defined set of components that includes free ions such as Na+ and neutral and charged complexes (e.g., H4SiO40, Cr(OH)2+). The data base of reactions is written in terms of these components as reactants. An ancillary program, PRODEFA2, serves as an interactive pre-processor to help produce the required MINTEQA2 input files.

Several modifications important to the user have been made since the last publication of a MINTEQA2/PRODEFA2 user manual Two documents supplement the original user's manual file (USERMANU.PDF) and are included--along with the original user's manual--with the release of versions 4.01 and 4.02 of the MINTEQA2 model system. The file:
  • SUPPLE1.PDF supplements the basic information in the version 3.11 user's manual and describes significant changes since version 3.0
  • SUPPLE2.PDF outlines the development of the data base of diffuse-layer sorption reactions for hydrous ferric oxide (HFO) to be used in equilibrium speciation calculations for the Hazardous Waste Identification Rule (HWIR)

Significant changes in the MINTEQA2/PRODEFA2 model since the publication of the version 3.11 user manual include: Incorporation of the Gaussian model for computing trace metal complexation with dissolved organic matter, modifications to minimize the occurrence of violations of Gibbs phase rule, modifications to allow direct simulation of a titration in one model run, modifications to allow selected output to be written for easy importing to a spreadsheet, modifications to improve model execution speed and convergence, and modifications to improve the thermodynamic data base used by the model, including the addition of beryllium (II), cobalt (II and III), molybdenum VI), and tin (II and IV) compounds. Also, errors in thermodynamic constants associated with certain metal-organic reactions in earlier versions have been corrected in version 4.01, thermodynamic constants for inorganic species have been reviewed and updated, and all reference citations for equilibrium constants have been included in the revised data base. These and other revisions are described in the file SUPPLE1.PDF.

The file SUPPLE2.PDF outlines the development of the data base of diffuse-layer sorption reactions for hydrous ferric oxide (HFO) to be used in equilibrium speciation calculations for the Hazardous Waste Identification Rule (HWIR). The sorption of contaminant metals and metalloids is important in that it retards contaminant transport in the subsurface. In HWIR, the results of the speciation modeling are used to compute the contaminant sorption distribution coefficient, Kd, a transport model parameter that must be included to account for this retardation. The contaminant metals and metalloids of interest in HWIR are: arsenic (As), antimony (Sb), barium (Ba), beryllium (Be), cadmium (Cd), chromium (Cr), cobalt (Co), copper (Cu), lead (Pb), mercury (Hg), molybdenum (Mo), nickel (Ni), selenium (Se), silver (Ag), thallium (Tl), tin (Sn), vanadium (V), and zinc (Zn). Although not a metal, cyanide (CN) is also of interest as a transportable contaminant. A consistent set of sorption reactions are presented for all HWIR contaminants of interest. The corresponding MINTEQA2 data base is also presented in this file.

Keywords: aquatic biology, assessment, compliance, metals, NPDES, permits, test/analysis
Model Technical Contact Information:
Agency Contact:
Dr. Nick Loux
CEAM Help Desk (Group CEAM, 706 355 8403)
Office of Research and Development
National Exposure Research Laboratory
Center for Environmental Assessment Modeling (CEAM)

(706) 355-8400

The model was developed by Jerry D. Allison of Computer Sciences Corporation.

Model Homepage: http://www.epa.gov/ceampubl/mmedia/minteq/index.html
Substantive Changes from Prior Version: http://www.epa.gov/ceampubl/mmedia/minteq/mintreln.html
Plans for further model development: MINTEQA2-Nano – inclusion of a new electrostatic adsorption model for spherical and cylindrical particles.

User Information Back to Top
Technical Requirements
Computer Hardware
Standard MS Windows systems. http://www.epa.gov/ceampubl/mmedia/index.html
Compatible Operating Systems
Windows 98, NT, 2000, XP

Can be used on workstations and mainframes if distributed Fortran source code is loaded.

Download Information
This model is available for download at http://www.epa.gov/ceampubl/mmedia/minteq/index.html
Using the Model
Basic Model Inputs
Included in installer User provides analytical concentrations of various water chemistry parameters.
Basic Model Outputs
Aqueous equilibrium speciation of ionizable species. Partitioning behavior also is generated in some cases.
User Support
User's Guide Available?
Yes, included in installer and accessible from web page.
Other User Documents
http://www.epa.gov/ceampubl/mmedia/minteq/SUPPLE1.PDF http://www.epa.gov/ceampubl/mmedia/minteq/SUPPLE2.PDF

These and other user documents (MMHG&TBT.pdf, readme, abstract, release notes) are also packaged into installer.

Availability of User Support
8-5, M-F (CEAM Help Desk)
User Qualifications
MINTEQA2 is among a number of available geochemical speciation models. A basic knowledge of chemistry is required and coursework on geochemical speciation modeling is very helpful.

Model Science Back to Top
Problem Identification
The environmental behavior of metals/metalloids is quite complex. Geochemical speciation models such as MINTEQA2 provide insight as to whether ionizable contaminants will experience redox, complexation, adsorption and/or precipitation reactions with those chemical species commonly observed in natural waters.
Summary of Model Structure and Methods
The user provides aqueous analytical data and the model simulates their possible chemical reactions. The output then provides estimates of the aqueous speciation under equilibrium conditions.

The model accesses a large database of published thermodynamic reaction constants to predict the simultaneous equilibrium distribution of user supplied analyte concentrations in a given aquatic system.

Governing equations are solved numerically.

Model Evaluation

The model has been internally peer reviewed by EPA Science Advisory Board (SAB) and ERD-Athens internal review panels.

Model has been externally peer reviewed via publications in the technical literature.

Publications concerning MINTEQA2 are too numerous to mention. Prospective users should perform a web search on MINTEQA2.
Key Limitations to Model Scope
The model provides estimates of thermodynamic equilibrium speciation; those natural aquatic phenomena not governed by thermodynamic controls are poorly simulated (e.g., many redox reactions).
Case Studies
Easily found by performing a web search on MINTEQA2.

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