Extending the overlay and index methods: A new modeling approach for the assessment of groundwater vulnerability

The aim of this work is to improve the existing overlay and index method for aquifer vulnerability assessment with a novel procedure, a “hybrid” method, that is not limited to the vertical transport through the vadose zone but considers also the horizontal transport through groundwater. Based on simplified probabilistic analysis, we use any overlay and index method to assess the probability that the contaminant reaches the groundwater; such probability is propagated within the aquifer using the piezometric surface as proxy of the groundwater flow. For this purpose, we make use of geomorphological methods, usually available in Geographic Information Systems (GIS) software. This analysis leads to the definition of a combined vulnerability index υ, a new index that embeds information on all the possible contaminant transport paths from soil surface, up to a given position including information on the vadose zone. The procedure is standardized through the use of QGIS software; as an application example the procedure is applied to a groundwater catchment area in the Campania region (Southern Italy). The method is independent from the index and overlay method used and the hydraulic characteristics of the aquifer. Moreover, this procedure requires a few data and it can be used to analyze large areas, showing its effectiveness in the assessment of the intrinsic groundwater vulnerability.
The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)