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The Iceland Water Chemistry Group presents the chemical speciation program

The computer program WATCH is used to calculate aqueous speciation in natural waters. Its primary area of application is to geothermal fluids, but it is useful for non-thermal waters as well.

The program reads chemical analyses of water, gas, and steam condensate samples collected at the surface and computes the chemical composition of downhole, or aquifer, fluids at some suitably chosen reference temperature. This includes the pH, aqueous speciation, partial pressures of gases, redox potentials, and activity products for mineral dissolution reactions.

The background to the program and the general methods of calculation used were described by Stefán Arnórsson, Sven Sigurdsson, and Hördur Svavarsson in their 1982 paper

The chemistry of geothermal waters in Iceland. I. Calculation of aqueous speciation from 0°C to 370°C.
Geochimica et Cosmochimica Acta, vol. 46, pp. 1513 – 1532.

The paper gives references for the original thermodynamic data used. A few of the dissociation constants and some of the Henrys constants have been updated since, as noted in the program description.

Previous versions of this program have been used by the geothermal community worldwide for nearly three decades. Version 1, which comprised two distinct programs, came out in 1981. It was in use until about 1994, at which time it was superseded by version 2.1. This newer version constituted a rewrite of the original code from scratch, and the two older programs were conflated. Version 2.2 came out in 2002, and 2.3 in January of 2004, both representing minor improvements and bug fixes. The present version, 2.4, was released in April 2010.

The WATCH program is available for both the Linux and the Windows operating systems. A companion program, WAIN, is used to create input data files.

For Windows:

To run these programs you also need cygwin1.dll.

This library must be extracted from the zip file and placed on an accessible path. It should thus preferably be copied into the folder c:\windows\system32 or the folder c:\winnt\system32, as appropriate.

The file watch_readme.pdf contains a brief program description and user guide.

For Linux:

To make these files executable you may need to run chmod +x watch24 and chmod +x wain12 after downloading.

The file watch_readme.pdf contains a brief program description and user guide.

Questions about the program may be addressed to Jón Örn Bjarnason.