A mathematical model presented in this paper describes the dispersion and concentration of contaminants (fine and coarse) in porous medium with the effect of chemical reaction. Solute transport in porous media is discussed by means of advection-dispersion equation. The effect of particle mass parameter and reaction rate parameter on the dispersion coefficient and mean concentration of a chemical solute is studied by introducing a slug of finite length. Analytical solutions are obtained by varying the dimensionless time, axial distance and length of the solute. The results are depicted using graphs.