LLNL Yucca Mountain project - near-field environment characterization technical area: Letter report: EQ3/6 version 8: differences from version 7

EQ3/6 is a software package for geochemical modeling of aqueous systems, such as water/rock or waste/water rock. It is being developed for a variety of applications in geochemical studies for the Yucca Mountain Site Characterization Project. The software has been extensively rewritten for Version 8. The source code has been extensively modernized. The software is now written in Fortran 77 with the most common extensions that are part of the new Fortran 90 standard. The architecture of the software has been improved for better performance and to allow the incorporation of new functional capabilities in Version 8 and planned subsequent versions. In particular, the structure of the major data arrays has been significantly altered and extended. Three new major functional capabilities have been incorporated in Version 8. The first of these allows the treatment of redox disequilibrium in reaction-path modeling. This is a natural extension of the long-running capability of providing for such disequilibrium in static speciation-solubility calculations. Such a capability is important, for example, when dealing with systems containing organic species and certain dissolved gas species. The user defines (and sets the controls for) the components in disequilibrium. Such corrections can now be made if the requisite data are present on a supporting data file. At present, this capability is supported only by the SHV data file, which is based on SUPCRT92. Equilibrium constants and other thermodynamic quantities are correct1961ed for pressures which lie off a standard curve, which is defined on the supporting data file and ordinarily corresponds to 1.013 bar up to IOOC, and the steam/liquid water equilibrium pressure up to 300C. The third new major capability is generic ion exchange option previously developed in prototype in a branch Version 7 level version of EQ3/6 by Brian Viani, Bill Bourcier, and Carol Bruton. This option has been modified to fit into the Version 8 data structure, which allows avoidance of some problems that occurred with the prototype. This capability allows the user to define exchange phases with multiple sites, specifying the exchange reactions and relevant thermodynamic data. Some minor improvements have also been made. The major option switch arrays for EQ3NR and EQ6 (iopt, iopr, iodb) have been made identical for both codes (though some elements may only pertain to one code or the other). EQ3NR now accepts alkalinity in units of mg/L equivalent CaCO3, in accord with the usual method of presenting data for groundwater chemistry. A previous treatment of alkalinity had been removed from the Version 7 series. Supporting data files may now utilize temperature-pressure grids with arbitrary numbers of temperature ranges and temperature points per range, instead of the old EQ3/6 standard of two temperature ranges with four and five points (one point being common to both temperature ranges). Version 8 of EQ3/6 also includes utility codes to convert EQ3NR and EQ6 input files from version levels 7 and 7.2 level to version level 8