Allocca, Pasquale (2026) Valutazione della vulnerabilità intrinseca e specifica degli acquiferi mediante modellazione multiscalare, parametrica e numerica. [Tesi di dottorato]

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Abstract

Study areas: Alluvial, volcanic, and conglomerate aquifers of the experimental sites of the PNRR Agritech Project. Study focus: In the framework of the PNRR Agritech project, the PhD thesis was focused on three main objectives: i) the assessment of intrinsic vulnerability to groundwater pollution of Agritech experimental sites, located in northern and southern Italy (e.g., Veneto, Emilia-Romagna, Campania and Basilicata regions), using two different index-based approaches and a GIS-based analysis of geological, hydrogeological, meteorological, land use and agronomical data to develop a tool useful to decision-makers and farmers to the planning and managing agricultural activities; ii) the multi-scale and multi-parametric characterization of the Torre Lama experimental site (Campania region), aimed to implement an innovative and effective methodological approach based on the monitoring and numerical modeling of unsaturated and saturated zones of a complex multi-layered semiconfined alluvial aquifer system; iii) the assessment of the specific vulnerability to groundwater pollution by pesticides of the Torre Lama experimental plot, using process-based and parametric approaches implemented in Hydrus-1D and QGIS environment, by a detailed characterization, quali-quantitative monitoring and modeling of groundwater and pesticides transport in the unsaturated and saturated zone. Results: The Agritech experimental sites are characterized by an intrinsic groundwater vulnerability to pollution ranging from medium to very high degree, as indicated by the application of the SINTACS method, and from moderate to very high degree, as estimated by Pesticide DRASTIC LU method. The alluvial aquifers are characterized by a general high degree of groundwater vulnerability to pollution. This result is due to the geological, hydrogeological, geomorphological, pedological and land use characteristics as well as the agricultural and agronomic activities. The Torre Lama pilot site, chosen as representative of many inland and coastal alluvial plain areas in Italy and Europe, is characterized by a very complex alluvial aquifer system, which hosts a multi-layered aquifer system whose semiconfined groundwater flow into sandy and gravelly horizons is separated by aquitards consisting of silts and clayey layers. At the scale of the Torre Lama pilot site, six distinct semiconfined aquifer horizons were recognized, although some of them having equal potential piezometric levels. Consequently, within the complex multilayered alluvial aquifer system, two mains potential piezometric levels can be distinguished up to 32 m b.g.l.: a first potential piezometric level referred to the shallow semiconfined aquifer (with potential piezometric head about 43,0 m a.s.l.) and a second potential piezometric level referring to the deeper semiconfined alluvial aquifer (with potential piezometric head about 34,8 m a.s.l.). For both shallow and deeper semiconfined aquifers, groundwater flow is oriented towards SE with average hydraulic gradients about 6,70×10-3 and 2,33×10-2, respectively, and locally drained by the Lama torrent. The multi-scale and multiparametric methodological approach, by field and laboratory investigations, as well as by a multi-level groundwater monitoring in the vadose and saturated zones, allowed the reconstruction of the geometry, and structure of the unsaturated and saturated zone of multilayered semiconfined alluvial aquifer systems and the understanding of the complex groundwater circulation. At the site-specific scale, a permanent hydrological observatory was built within the Torre Lama pilot site which allowed to test same hydrological processes (i.e., infiltration, evapotranspiration, percolation and transport of pesticides through the unsaturated zone) by multiparametric monitoring and numerical simulation of water flow and contaminant migration in the vadose and saturated zones. Numerical modeling by Hydrus-1D code has allowed the estimation of the unsaturated travel time of three pesticides (Florasulam, Pinoxaden and Clodinafop-Propargyl), among those most used in wheat cultivations, which is considered expressing the specific groundwater vulnerability to pollution of the shallow semiconfined alluvial aquifer of the Torre Lama experimental site. The unsaturated travel time at a depth of 5 m b.g. range from 2447 and 2987 days, equivalent to velocity of pollutant transport of 2,31×10-8 and 1,85×10-8 m/s (0,0019 and 0,0015 m/d) for Florasulam and Pinoxaden, respectively. Moreover, the different behavior of Clodinafop-Propargyl, comparable to an immobile pollutant, gives the scientific evidence supporting decisions aimed at a sustainable, “zero pollution” agriculture. The long travel times for the pesticides simulated in the Torre Lama experimental plot results in a low specific groundwater vulnerability to pollution of shallow semiconfined alluvial aquifer. This is in agreement with the groundwater vulnerability to pollution at the plot scale evaluated by Pesticide DRASTIC LU_mod method. These results were validated by a comparison with the data of multilevel hydrochemical monitoring. Good hydrochemical quality of the groundwater coupled with very low concentration of pesticides (always <0.05 μg/L) in the groundwater of the saturated zone show that the local impact of agronomic practices is negligible, although some anomalous concentrations of heavy metals (e.g., arsenic and beryllium) may be attributable to other natural and anthropogenic factors. In conclusion, the PhD thesis offers important methodological insights for a novel research in the hydrogeological and agronomic fields, aimed at finding a better balance between environmental, economic, and social sustainability for a modern agriculture. Therefore, results obtained by the PhD thesis represent new scientific instruments and operational tools, technologically and methodologically innovative and easily exportable and applicable to other environmental and agronomic contexts, capable of supporting decision-makers and users in the planning and management of agronomic activities, offering more sustainable solutions from an environmental, agronomic, and economic point of view.

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