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W S Hitchcock, Inc.
Hydrochemical Modeling

Site characterization requires a thorough understanding of the nature and extent of contamination. This understanding must include a physical model that explains the sources of contamination, the spread of contamination, and the likely chemical fate of contamination. Such a physical model is extremely useful for risk assessment, for determination of remediation options and for assignment of liability for environmental damages.

Powerful computer programs (such as the U.S. Geological Survey's PHREEQC) allow one to calculate: speciation, saturation-index, reaction-path and advective-transport, mixing of solution, mineral and gas equilibria, surface-complexation reactions, ion-exchange reactions, and inverse modeling (which finds sets of mineral and gas transfers that account for compositional differences between aquifers).

Although PHREEQC's database contains a large amount of thermodynamic data, complete understanding of the chemical composition of the aquifer is required. Input data include:

Major and trace ions,
Alkalinity,
eH,
pH,
Temperature,
Partial pressure of gases, and
Aquifer geology.

Interpretation of the modeling results from such programs requires a thorough knowledge of chemical equilibrium and physical/chemical processes.

 

The US Geological Survey's computer program for speciation, reaction-path, advective-transport, and inverse geochemical calculations is available on the world wide web.

  PHREEQC

Documentation for PHREEQC is in PDF format. If you need a viewer for PDF files,

  Adobe Reader is available for free download.

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W S Hitchcock, Inc.
Last update: August 31, 2003.