One of the most important problems in many dams is the seepage of water through the foundation and abutments. The study of different solutions for sealing, especially in earth dams and desinging a proper plan for sealing the foundation and abutments, has a major effect on the project integrity from technical and economical viewpoints. In this regard, the sealing of Kalghan Chai dam site has been studied, considering the presence of a 70m thick alluvial terrace at the right abutment. This has caused engineering geological and technical difficulties. So by doing exploratory geological and geotechnical investigations and making considerable insitu and laboratory tests, a combination of grout curtain, cutoff wall and clay blanket is determined as the best sealing elements for Kalghan Chai dam site. This plan inclues a cutoff wall (about 120m of length and 25m in depth) at the right abutment trought the alluvial terrace, a grout curtain in the left abutment and the river bed and finally a clay blanket on the right abutment that conects the clay core on the surface to the intact rock at the upstream.