The interest in the low-enthalpy geothermal resources is growing, owing to its wide availability, and the possibility of overcoming the problems related to energy storage. Among the low-enthalpy plants, the installation in coastal areas of the open-loop groundwater heat pump (GWHP) systems, that use groundwater as the geothermal fluid, is particularly attractive because of the presence of shallow aquifers. Nevertheless, these aquifers are often affected by seawater intrusion, so strict monitoring before GWHP installation is needed to check the feasibility of the plant. This work reports a detailed quali-quantitative characterization of a costal aquifer, in Southern Italy, for its exploitation as a very low enthalpy geothermal resource. The main groundwater parameters were monitored to assess the groundwater suitability to be used as geothermal fluid. A long-term pumping test, simulating the designed open-loop GWHP system, was performed to evaluate its potential impact on seawater intrusion. The results revealed that the open-loop GWHP plant do not affect the quali-quantitative equilibrium of the studied coastal aquifer. Furthermore, the study demonstrated that the used methodological approach is proper for the early assessment of the feasibility of the GWHP plant without affecting the seawater intrusion processes, and with minimum impact.