Sulfate and chloride attack for underground R.C. constructions is an important subject of many researchers. Chemical attack by aggressive waters specially sewage is one of the factors causing deterioration and corrosion damage of concrete in the underground R.C. elements . The chemical resistance of R.C. elements against chloride and sulfate attack induced by sewage water is expressed by the percentage of their mechanical property losses. Sulfate attack of concrete building foundations induced by sewage water was studied in the field. Effect of the diffused salts concentration by sewage waters from multiple seepage pits through a confined porous media on the load carrying capacity of underground R.C. columns was analytically studied. But, the influence of chloride and sodium sulfate solutions diffused by sewage water through unconfined porous media on the expected deterioration and corrosion damage of underground R.C. elements after a long period of time, specially footings and necks of columns, has not been enough studied . So, in this paper is developed an analytic model for the effect of the induced chloride and sodium sulfate salts by sewage water through unconfined porous media on the future corrosion damage and deterioration of concrete in underground R.C. elements specially columns. The finite difference technique is used and a computer program is developed and written in a basic language to compute the future mechanical properties losses of R.C. elements exposed to sewage water for a long period of time. Analysis of the numerical results shows that, the expected deterioration and corrosion damage of any underground R.C. elements exposed to sodium sulfate and chloride solutions flow induced by sewage water depend mainly on the time of exposure to these salts, radial distance of the concrete structure from the sewage resources and their number, height of the sewage water solution and its relative concentration at that structure. The difference between the values of of “CFc" and “Єcf “ for unconfined and confined porous media decreases gradually and slowly with increasing time until reaching equal value ( CFc = 0.696, Єcf =5.48x10-4) after 8 years. The unconfined porous media properties (k,ф) and total relative concentration "Ca/Co" of diffused chloride and sulfate salts at that structure have not any effect on its mechanical properties losses .