Re: INFORMATION ABOUT WATEQ

["David L Parkhurst" <dlpark@xxxxxxxx>]

> Iam happy to send you my 1st e-mail. I want your help to show me how I
can use WATEQ and what WATEQ can tell me if  I used it with my data about
high saline water. I have no information about this programme I need to
know the steps by which I can use the results to identify my water analysis
results.

WATEQ is a speciation code, that is, it calculates the distribution of
elements among aqueous species (ion pairs and complexes). The usual reason
for doing the calculation is to obtain saturation indices for minerals and
partial pressures of gases, which whether minerals (and gases) should
dissolve or precipitate in the solution. The program needs a complete major
element chemical analysis (Ca, Mg, Na, SO4, Cl, alkalinity, and field pH)
to make the calculation.

I would suggest using PhreeqcI instead of WATEQ if you are running on a
Windows computer. You can download PhreeqcI from
https://wwwbrr.cr.usgs.gov/projects/GWC_coupled/phreeqc. It has more
features that WATEQ and is interactive.

High salinity may be a problem. Both WATEQ and PhreeqcI use an
ion-association model. It is not accurate at high ionic strengths. The
range of applicability is up to 0.1 to 1.0 molal ionic strength, depending
on the composition of the waters. Another approach, called the specific
interaction or Pitzer approach, is better for higher ionic strengths.
However, this approach is limited to major ions and does not allow for
redox or alumino-silicate reactions. We have a program called PHRQPITZ at
the same web site, but it is old and difficult to use. You may be able to
use other geochemical models that include the Pitzer approach (TEQUIL,
EQ3/6, Geochemists Workbench), but I'm not sure these programs are easily
available.

David


David Parkhurst (dlpark@xxxxxxxx)
U.S. Geological Survey
Box 25046, MS 413
Denver Federal Center
Denver, CO 80225