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Water Quality Models

Cornell Mixing Zone Expert System (CORMIX)

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CORMIX is a water quality modeling and decision support system designed for environmental impact assessment of mixing zones resulting from wastewater discharge from point sources. The system emphasizes the role of boundary interaction to predict plume geometry and dilution in relation to regulatory mixing zone requirements. As an expert system, CORMIX is a user-friendly application which guides the water quality analysts in simulating a site-specific discharge configuration. To facilitate its use, ample instructions are provided, suggestions for improving dilution characteristics are included, and warning messages are displayed when undesirable or uncommon flow conditions occur.

Cormix contains three major subsystems. The first subsystem, CORMIX1, is used to predict and analyze environmental impacts of submerged single port discharges to lakes, rivers, and estuaries. The second subsystem, CORMIX2, may be used to predict plume characteristics of submerged multiport discharges. The third subsystem, CORMIX3, is used to analyze positively and neutrally buoyant surface discharges to lakes, rivers, and estuaries with a high degree of accuracy.

A mixing zone is a limited area where initial dilution of a discharge takes place and where numeric water quality criteria can be exceeded but acutely toxic conditions are prevented.

From the August 1994 EPA publication "Water Quality Standards Handbook: Second Edition" (EPA-823-B94-005a) (PDF format, 18MB) allowable mixing zone characteristics should be established to ensure that:

  • mixing zones do not impair the integrity of the water body as a whole,
  • there is no lethality to organisms passing through the mixing zone, and
  • there is no significant health risk considering likely pathways of exposure.
Also mixing zones should not be permitted where they may endanger critical areas (e.g. , drinking water supplies, recreational areas, breeding grounds, areas with sensitive biota).

In contrast, the regulatory mixing zone is a definition which allows for the initial dilution of a discharge rather than imposing strict end-of-pipe concentration requirements for NPDES water quality permits for conventional and toxic discharges.

In theory, the regulatory mixing zone may therefore allow for efficient natural pollutant assimilation. In practice they can be used as long as the integrity of a water body as a whole is not impaired.

Lauren MacWilliams is the primary contact for CORMIX support services. The Oregon Graduate Institute of Science and Technology (OGI), under a cooperative agreement with EPA, provides CORMIX information, distribution, and technical support services to the CORMIX user community. The CORMIX home page exit EPA contains updated information about software releases, model applications, and tools for regulatory mixing zone decision support. The P. I. for the OGI/OST cooperative agreement is Dr. Robert L. Doneker (503) 748-4053 at the Department of Environmental Science and Engineering, Oregon Graduate Institute.

 

 

 
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