Underground dams are considered one of the effective approaches for groundwater conservation and water resources management in arid and semi-arid regions. The feasibility and long-term performance of these structures strongly depend on geological, hydrogeological, and geotechnical conditions. This study was conducted to evaluate the engineering geological and geotechnical characteristics of the Pasband underground dam site in Lamerd, southern Iran. Six boreholes were drilled and a comprehensive field and laboratory investigation program was carried out. The investigations included geological mapping, Rock Quality Designation (RQD), permeability tests, grain-size analyses, Atterberg limits, direct shear tests, and groundwater quality assessments. The results indicated that the bedrock consists mainly of marl and limestone formations with favorable engineering properties. RQD values generally exceeded 60%, indicating good rock quality. Hydraulic conductivity values ranged between 10⁻⁵ and 10⁻⁴ cm/s, demonstrating limited seepage potential. The alluvial deposits showed acceptable shear strength with internal friction angles ranging from 33° to 39° and cohesion values between 0.02 and 0.08 kg/cm². Groundwater quality analyses revealed EC values of 755–783 μS/cm, TDS values of 363–365 mg/L and neutral pH conditions. Overall, the results confirm the suitability of the Pasband site for underground dam construction and long-term operation.