Dissolution of gypsum and anhydrite at the foundation of Mosul Dam continued after its construction since 1986 onwards. After impounding, acceptable residual permeability could not be reached and new areas of high grout takes appeared in some other locations. New grout mixes were tested and even methods of delivering and injecting large grout quantities were developed. Sandy mixes were developed by adding certain weight of sand to the cement mix. In addition, pouring gravel after completion of grouting in large takes' zones was performed. As a result of gravel addition, it was concluded that it was not effective and very difficult to pour. Massive grouting was used where bentonite was added to the mix. Piezometric observation was used for checking the conditions of the grout curtain and the detection of problematic areas where additional treatment was required. Massive grouting, however, did not stop the dissolution processes altogether and it seems that it is not likely to do so in the future. The continuation of this program year after year does not preclude some bad implications. More research work is required to improve massive grout durability by adding chemicals which may interact with gypsum beds and hinder dissolution. This can help to improve gypsum resistance and increase its stability. Mathematical models might also be used to understand the mechanism of cavities formation and collapsing.