PhreeqcUsers Discussion Forum
Conceptual Models => Equilibrium assumptions => Topic started by: IliasBouchkira on July 18, 2019, 09:42:32 AM

hello,
please can anyone help me to find the equation used by phreeqC to estimate water activity
thanks you in advance,

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 3.4.012927\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

Thank you very much