transform hydrauluc head

Hello!
I am trying to simulate a seawater intrusion problem.
At the coastline nodes, I transformed the saltwater hydraulic head to the equivalent freshwater hydraulic head. I used the sea concentration in Cl to calculate the density ratio, and I used the intended equation.

In my region, few kilometers away from the coastline,  exist some wells with high concentration of Cl. Those concentration are inported to my model as initial mass conditions. I want to transform again their saltwater hydraulic head to the equivalent freshwater hydraulic head, to define initial coditions.  Each one of this wells has different concentration of Cl.

Also, after the simulation results, I want to transform again the equivalent freshwater hydraulic head, to saltwater hydraulic head , because I want to compare the results with my data.

Have I to use the same equation as in boundaries condition? Have I to use the same value of density ratio in that equation?

Waiting for your answers
Thank you

The basic equation is always the same. However, at the boundary condition you assume that the concentration is constant over depth. That's probably not the case for the observation wells, so that the correction for getting freshwater head would depend on depth and would have to be done separately for each slice.

the correction you need to apply is depend on the water (density) that are actuaaly occuping the volume of the well pipe.
if the well "sample" only salt water of homogenous density it is easy to correct.
if the well "sample" fresh water over salt water you  should correct only the salt water interval (i.e. from the interface to the well bottom).
if there is other vertical distribution of salinity then consider integration.
good luck!

Thank you for your help!!!