surfaces in PHREEQC

[Mdodds0408@xxxxxxx]

Hi David,

I have a final question about surfaces in PHREEQC.  I defined an organic 
surface for VOCs to sorb to.  The three numbers that define the surface are 
(a) the number of moles of sites for sorption, (b) the specific surface area, 
and (c) the mass of the surface.  However, when I explicitly define the 
number of moles of sites for sorption that 1L of water would partition to in 
an aquifer with a certain fraction of organic carbon, the other two numbers 
don't make a difference (I've varied them extensively and I've seen no 
sensitivity to those parameters).  Is another way to do this?  For example, 
can I not explicitly define the number of moles of sites for sorption and do 
this based on the mass and the specific surface area?  Additionally, how does 
PHREEQC treat the K given for the sorption reaction?

As always, thanks so much for your help!
Margaret