Canadian Environmental Modelling Centre


Version 3.10 - February, 2007

New in version 3.10!

The "Quantitative Water Air Sediment Interaction" or "QWASI" model is designed to assist in understanding chemical fate in lakes.

It describes the steady state behaviour of an organic chemical in a lake subject to chemical inputs by direct discharge, inflow in rivers, and deposition from the atmosphere. Chemical is removed from the lake by evaporation, irreversible reaction in the water and sediment, outflow in the water, and sediment burial. The mass balance equations for the well-mixed water column and the well-mixed layer of surficial sediment also include sediment-water exchange by diffusion, deposition, and resuspension. The model, as supplied, treats PCBs in Lake Ontario.

Based on the following publications:

Mackay, D. 2001. "Multimedia Environmental Models: The Fugacity Approach - Second edition", Lewis Publishers, Boca Raton. pp. 201-213.

Mackay, D., Joy, M., Paterson, S. 1983. A Quantitative Water, Air, Sediment Interaction (QWASI) Fugacity Model for Describing The Fate of Chemicals in Lakes. Chemosphere. 12: 981-997.

Mackay, D., Paterson, S., Joy, M. 1983. A Quantitative Water, Air, Sediment Interaction (QWASI) Fugacity Model for Describing the Fate of Chemicals in Rivers. Chemosphere. 12: 1193-1208.

With a Great Lakes parameterization as described in:

Webster, E., Lian, L., Mackay, D. 2005. Application of the Quantitative Water Air Sediment Interaction (QWASI) Model to the Great Lakes. Report to the Lakewide Management Plan (LaMP) Committee CEMC Report 200501. Trent University, Peterborough, Ontario

Other related publications:

Mackay, D., Diamond, M. 1989. Application of the QWASI (Quantitative Water Air Sediment Interaction) Fugacity Model to the Dynamics of Organic and Inorganic Chemicals in Lakes. Chemosphere. 18: 1343-1365.

Mackay, D. 1989. Modelling the Long Term Behaviour of an Organic Contaminant in a Large Lake: Application to PCBs in Lake Ontario. J. Great Lakes Res. 15: 283-297.

Diamond, M., Mackay, D., Poulton, D. and Stride, F. 1994. Development of a Mass Balance Model of the Fate of 17 Chemicals in the Bay of Quinte. J. Great Lakes Res. 20: 643-666.

Diamond, M.L., Mackay, D., Poulton, D.J., and Stride, F.A. 1996. Assessing Chemical Behavior and Developing Remedial Actions Using a Mass Balance Model of Chemical Fate in the Bay of Quinte. Wat. Res. 30: 405-421.

Lun, R., Lee, K., De Marco, L., Nalewajko, C. and Mackay, D. 1998. A Model of the Fate of Polycyclic Aromatic Hydrocarbons in the Saguenay Fjord. Environ. Toxicol. and Chem. 17: 333-341.

Woodfine D.G., Seth R., Mackay D., Havas M. 2000. Simulating the Response of Metal Contaminated Lakes to Reductions in Atmospheric Loading Using a Modified QWASI Model. Chemosphere. 41: 1377-1388.

Mackay, D., Hickie, B. 2000. Mass Balance Model of Sources, Transport, and Fate of PAHs in Lac Saint Louis, Quebec. Chemosphere.41: 681-692.

Milford, L. 2002. A Multi-Segment Modelling Approach to Describe the Fate of PCBs in Two River Systems in Southern Ontario. Masters thesis, Watershed Ecosystems Graduate Program, Trent University, Peterborough, Ontario.

Warren, C.S., Mackay, D., Bahadur, N.P., Boocock, G.B. 2002. A Suite of Multi-Segment Fugacity Models Describing the Fate of Organic Contaminants in Aquatic Systems: Application to the Rihand Reservoir, India. Water Research 36:4341-4355.

Features of the QWASI Software

Provides a database of chemicals and chemical properties.
Permits temporary additions/changes of chemicals and their properties to a simulation.
Permits permanent additions, changes and deletions of chemicals and their properties to the chemical database. Provides a database for lake parameters.
Permits temporary additions/changes of lakes and their properties to a simulation.
Permits permanent additions, changes and deletions of lakes and their properties to the lake database.
Provides context-sensitive Help.
Displays and prints the QWASI model calculations, as performed by the program.
Allows the printing of simulation tables and the summary diagram.
Allows the program results to be saved as an comma separated value text file, easily viewed with standard spreadsheet software.

The required input data are:


  • chemical name
  • molar mass
  • data collection temperature
  • overall reaction half-lives in water and sediment
  • Type 1 chemicals

  • - water solubility
    - vapour pressure
    - melting point
    - log Kow
  • Type 2 chemicals

  • - partition coefficients


  • water surface area and total volume
  • depth of active layer of sediment
  • particle concentrations in the inflow water, lake water, aerosols in air, and volume fraction of solids in surface sediment
  • particle densities (suspended sediment, sediment solids, aerosols)
  • organic carbon fraction (suspended sediment, sediment solids, inflow suspended sediment, resuspended sediment)
  • water inflow and outflow rates (m3/h)
  • sediment deposition, resuspension and burial rates (g/m2 day)
  • atmospheric deposition parameters (aerosol dry deposition velocity, scavenging ratio, rain rate
  • mass transfer coefficients (volatilization - air side and water side, sediment-water diffusion)
  • Emissions and Inflows

  • direct discharges to the lake
  • concentration in inflow water and in air
  • Model output includes:

  • chemical properties, lake parameters, and chemical inputs to the system
  • Z and D values
  • fugacities, concentrations and amounts in each compartment
  • mass balances and residence times
  • details of process rates
  • a summary diagram
  • Minimum system requirements are an IBM-compatible PC running Windows 98 or XP. This model will not run under Windows NT or 2000.

    Also available are
    Version 2.80, released December 2002, and
    Version 3.00, released October 2005.
    For non-Windows users the BASIC, evaluative, QWASI model is available.

    Please read the QWASI SOFTWARE LICENSE before downloading the software. Use of the software constitutes your agreement to abide by the terms and conditions set out in the license agreement.

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    Last updated June 12, 2013.