In this paper we re-examined the transfer equation of radioactive substances in the ground and offer a more realistic transfer equation and other equations available for assessment of the ground contamination from radioactive-contaminated groundwater. The transfer equation takes into account kinematic and hydrodynamic considerations on mass conservation of mobile radioactive substances in a porous medium that typifies the ground. The other equations available for contamination assessment are concerned with deposition in contaminated areas and discharge flow of contaminants to the areas contiguous to contaminated area. The equations are derived on the understanding that disintegration of the radioactive substances adhering onto solids in the ground porous medium occurs as a sink term during the transfer of mobile radioactive substances. Finally, it is noted that the discharge of groundwater due to advective flow will be predominant in comparison to the discharge by diffusion.