We propose that the electrical resistance of a geomaterial-water-air mixture can be modeled fundamentally as parallel electrical resistances of the geomaterial, pore-water, and air-voids.  We will develop a fundamentals-based model of pore water conductivity and soil-water resistivity as a function of pore water chemistry.  These models will allow us to incorporate a fundamental mechanism for validating water quality and resistivity measurements and defining accurate values for acceptance criteria used for determining the corrosivity of geomaterials in metal-reinforced MSE walls.