Water activity equation

[IliasBouchkira]

hello,

please can anyone help me to find the equation used by phreeqC to estimate water activity

thanks you in advance,

[dlparkhurst]

The equation for the activity of water for ion association models is given on page 17 of the 1999 manual, usually installed in the directory C:\Program Files (x86)\USGS\Phreeqc Interactive 3.4.0-12927\doc for PhreeqcI. Also included in all distributions of PHREEQC programs and t the USGS publications warehouse https://pubs.usgs.gov/wri/1999/4259/report.pdf

The Pitzer model solves for the osmotic coefficient based on the Pitzer formulation. See Plummer and others (1988) https://pubs.usgs.gov/wri/1988/4153/report.pdf

[IliasBouchkira]

Thank you very much