P040 Test site for aquifer cross-hole investigation for hydrogeological purposes Summary 1 A test site for hydrogeophysical purposes has been designed; integrated geophysical investigation from boreholes and surface permitted to estimate with good accuracy the main geological features up to 25 meter in depth. Four boreholes were drilled in the area and prepared for cross-hole geophysical tomography. We discuss the monitoring by means of time lapse 2D electrical resistivity tomography of a salt water injection. Introduction We describe the preliminary results of a long-term project which aim is to evaluate the feasibility and efficacy of geophysical techniques for the geological