Resistivity and full-decay IP inversion for imaging a coastal aquifer prone to saline intrusion: The Pontina Plain case study (Central Italy)

Many coastal areas are affected by groundwater salinization due to the unsustainable use of groundwater resources. For a cost-effective quantitative assessment of groundwater resources, electrical resistivity (ER) tomography is often used as a standalone geophysical technique. In this paper, we present an application of the integration of direct-current ER and full-decay-induced polarization (IP) method at the Pontina Plain (Central Italy). The case study is a coastal area in Central Italy prone to salinization due to both geological and anthropogenic factors. To achieve these goals, we inverted full-decay time-domain electrical data for Cole-Cole parameters. The resulting multi-parameter model provides a first approximation prediction of the permeability, employing well-established empirical relationships with the electrical parameters. We demonstrated that our approach: (i) can locate highly conductive zones directly related to saline intrusion inland using the resistivity as a fast proxy; (ii) can remove the ambiguity in the detection of clay/silt layers in the near-surface; and (iii) permit a prediction of the permeability, employing full-decay inversion of time-domain electrical data. However, the extremely conductive environment prevents the use of IP data for the reconstruction of deep layers or detection of the salt wedge front. Therefore, this approach can be used for hydro-geophysical screening and monitoring of salinization-prone sites, where strong limitations to direct inspection exist due to external constraints (e.g., protected lands).