At the initial state of my case study, the salt water has already intruded inside the aquifer. I have measurements for hydraulic head at different observation points covering the aquifer. As I understood from the manual (I’m a beginner) that an equivalent hydraulic heads should be inserted as input either at boundary conditions or for observation wells. I could calculate the equivalent at the boundary condition because its seawater with known density, however over the aquifer its brackish water and I don’t know the density and do know the salinity. How I could insert the measurements correctly?.