Leakage in engineering structures is considered as one of the main issues. Analysis of the amount of water leakage can be useful in preventing such events. Deriner Dam consists of a concrete arch dam with ancillary structures including tunnels, and an underground powerhouse with an installed capacity of 670 MW. Leakage was observed on the powerhouse after the construction stage. For this purpose, a number of geotechnical data (including rheological and mechanical properties of the grout mixes) were re-assessed to examine the source of leaking. For determination of leakage source, graphics of grout curtain were prepared by using grouting charts with the RockWorks v.16 program. Leakage zones were obtained according to the prepared graphics and showed on 3D model. The results show that temperature variation of grouting mixes is the primary cause of leakage and its effect observed in the underground powerhouse wall of the Deriner Dam.