Today, dams play vital infrastructure role in modern civilizations. For preventing the unfortunate failure during dam construction and operation, the frequent surveillance of dam safety should be considered. In the Gheisaragh dam, due to prevalence of solution in the foundation, the remedial cutoff wall was constructed. Regarding to some practical limitations and more critical condition, the cutoff wall is sketched in the middle and the right abutment of the foundation and extending over the left abutment is postponed to future requirements. This paper aims to evaluate seepage behavior of the dam foundation in the left abutment and if any, makes a decision for remediation requirements. Hence, the long-term data of piezometers and observation wells installed in the left abutment foundation are investigated. Besides, the anticipated seepage pattern of dam foundation is determined from 2-D finite element transient seepage analysis and compared with measurements. The results indicate that in both numerical and monitoring analyses, the water level in piezometers is considerably affected by the reservoir fluctuation after a short delay due to the short length of seepage paths in the foundation. However, after drawing down the reservoir, significant falling is observed in the piezo-metric water level with more intensity in comparison with the numerical analysis. Besides, the ground water level in the downstream of left abutment is considerably dropped and lies in hydrostatic condition. These consequences are inferred that the ground of the dam in left abutment has less ability to retain the water and thus, some open channel with higher permeability exist on the foundation. Therefore, the covering the left abutment of the dam foundation with the cutoff wall should be considered.
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