Geophysical and geochemical techniques to assess the origin of rising damp of a Roman building (Ostia Antica archaeological site)

A combined approach based on geophysical and geochemical analyses was carried out to determine the sources of rising damp in “Casa di Diana”, a Roman building located in the Ostia Antica archaeological site (Rome, Italy). The studied building is characterized by high humidity values (closed to saturation, > 90% RH) with significant efflorescence and sub-efflorescence phenomena on masonry walls. Electrical Resistivity Tomography was performed both inside and outside the building to understand the geological setting, to estimate the freshwater-salt water interface, to locate building foundations and consequently, to evaluate the interaction between the structural elements and groundwater. On the other hand, local shallow groundwater was analysed for soluble salts and isotopic analysis (δ18O) to identify the origin of solutes, to isolate the main factors determining the isotopic content and to investigate the aquifer behaviour in terms of movement and distribution processes. The water samples were collected from one well and one tank sited inside and outside the house, respectively. The geophysical inverted models, were able to detect a freshwater aquifer at the shallower depths (2–5 m) in correspondence to the Roman foundation walls (extended at depth up to 8 m), while below (8–10 m from surface) the salt water presence is likely. The chemical analysis confirmed that groundwater is slightly mineralized even though the salt concentration can be compatible with an interaction with sea salts, maybe due to the depth of the foundation walls. Therefore, the proposed approach is suitable for understanding the causal relationship between the observed phenomena, assessing the current degree of conservation of the archaeological site and consequently planning the recovery actions.