In the Treviso province (Veneto, Italy) most of the drinking water (nearly 60 %) is supplied from wells located in the northern piedmont area, where agricultural activities are developed using chemical plant protection products (chemical PPPs). In this area the aquifer interested by the groundwater extraction is unconfined, making the subsurface water resource intrinsically vulnerable to any PPP or PPP residue (metabolite) leaching from the agricultural soil to the groundwater table, and raising concerns about the consequences of a possible groundwater contamination on the health of the local inhabitants.To protect the drinking water resource, in 2019 the Veneto Region provided a technical framework for the definition of the wellhead protection areas (WHPAs, Resolution 1621) in accordance with the EU directives 2000/60 and 2006/118, related to the establishment of safeguard zones for the water bodies used for drinking water supply. In the WHPAs the use of PPPs is only allowed when accounting for the vulnerability of the groundwater and the well extracting water for human consumption. To define the vulnerability of wells supplying drinking water, a procedure that considers the tridimensional behavior of a possible contaminant is suggested, taking into account the mobility of the chemical species across the vadose zone, the total amount of PPPs applied on the soil, and combining the probability of contaminant infiltration with the groundwater pathlines reaching the well.An application has been developed in the piedmont area of the Treviso province where a geospatial analysis of the vine-specific PPPs sales data identified over 30 WHPAs potentially affected by the PPPs use. The 3D vulnerability assessment couples the position of the vulnerable WHPAs retrieved from the geospatial analysis with 1) the data related to the infiltration capacity of agricultural and not-agricultural unsaturated soils in the piedmont area of the Treviso province, 2) the mobility of the vine-specific PPPs, and 3) the groundwater pathlines in the superficial phreatic aquifer obtained by physically-based numerical modeling.This research has been funded by the contribution from the UNI-IMPRESA 2021 joint research project (Centre of Hydrology ‘Dino Tonini’ - University of Padua, Alto Trevigiano Servizi Spa, Piave Servizi Spa): Subsurface Water quality and Agricultural pracTices monitoring 2 (SWAT-2).

Recent studies have experimentally analyzed the leaching at local scale of some of the most diffused pesticides used in agriculture. To evaluate the vulnerability of wells supplying drinking water to PPPs used within wellhead protection areas (WHPAs), a map of vulnerability has been developed starting from the PPPs sales data in the Treviso province. The PPPs spatial distribution, obtained from the sellers’ locations and the extension of the cultivation areas was superimposed with the extension of the WHPAs, led to a vulnerability map, giving a clear picture of the wells that require PPPs-specific actions.

In the two-year period 2018-2020 the Centre of Hydrology ‘Dino Tonini’ of the University of Padova developed the UNI-Impresa research project SWAT (Subsurface Water quality and Agricultural pracTices monitoring) to study the interactions between agricultural practices, mainly those involved in the production of Prosecco, and the wellhead protection areas in the province of Treviso (Italy). Specific experimental activities, integrated by a modelling analysis of the collected data, were developed to understand the processes affecting the vertical evolution of a glyphosate-based pesticide in the unsaturated soil up to a depth of 0.70 m BGL. The pesticide, along with a non-reactive tracer (potassium bromide), was applied in November 2018 in two experimental sites (Settolo-Valdobbiadene and Colnù-Conegliano) organized nearby well-fields supplying public water systems. Its evolution subjected only to the natural hydrological forcing compared to the infiltration dynamics of the tracer was locally monitored by collecting and analyzing soil and water samples along six months. Both the application and the monitoring activities were carried out in each experimental site on two 25 m2 parcels located at reciprocal distances of 30 m (Settolo) and 115 m (Colnù), obtaining a detailed information about the glyphosate vertical evolution. Each point-wise analysis highlights a strong tendency of the pesticide and its principal metabolite (AMPA) to be adsorbed to the soil matrix rather than to be dissolved in the infiltrated rainwater and carried toward the deeper layers of the soil. However, high concentrations of the pesticide spotted at the depth of -0.70 m suggest that preferential pathways and more intense precipitation events enhance the downward movement of the glyphosate, either dissolved in water or adsorbed to microscopic particles. Differences in the pesticide spatio-temporal evolution were observed between parcels belonging to the same site.  Despite the decay analyzed during the experiments is related to both the chemical-physical properties of the soil, the potential movement is dominated by the heterogeneity of the hydraulic properties of soil. Hence, the evaluation of the infiltration capacity was considered a low-cost proper method to extend the analysis to the field scale (~102 m characteristic length). In the experimental site of Colnù, the spatial variability of the soil infiltration capacity (mm/min) and dynamics has been assessed developing a series of tests using the double ring infiltrometer in 17 different positions within an area of 1.75 ha. The investigated area extends over two contiguous vineyards inside the wellhead protection area. Two tests positions correspond to the site parcels while the remaining were spatially distributed maintaining reciprocal distances ranging between 15 and 50 meters. The measured soil infiltration capacity shows a large spatial variability, up to two orders of magnitude. The geostatistical interpolation (kriging) of the achieved data gives a quantitative estimation of the soil vulnerability at the field scale based on the potentially infiltrating pesticide.

Evidence of pesticides leaching due to intense rainfall events was found in two wellhead protection areas (WHPAs) located in the wine-growing areas of the Veneto piedmont area, in Italy. In this territory, the extensive agricultural activities related to the Prosecco production are developed often using pesticides-based vine protection practices. In the same area, numerous wells extract from the phreatic aquifers the drinking water needs of most of the province of Treviso, rising concern on the possibility of groundwater contamination from pesticides and risks for human health. Further experimental surveys – infiltration tests and soil samplings – were developed in the same WHPAs to study the spatial variability of the chemical-physical properties of the soil governing the pesticides leaching. The experimental data collected on areas of 2 hectares comprising both vineyards and non-agricultural areas, highlighted a larger variability of the soil properties inside the vineyards. Moreover, soil infiltration capacity, assumed in our case as the main property governing the pesticide leaching capacity, showed values up to one order of magnitude higher within the areas destined to wine-growing activities than the non-agricultural ones. This information, obtained at the local and at the field scale, were included in a geospatial analysis related to the distribution of vine-specific pesticides at the scale of the Treviso province, to obtain a vulnerability map for all the wells located in area. The geospatial analysis, developed in a geographical information system (GIS), is based on the sale data of pesticides for agricultural activities - also referred to as plant protection products (PPPs) – registered in the province in the period 2012-2019. The units of PPPs (kilograms or liters) collected at the municipal scale (the province of Treviso counts 94 municipalities) were analyzed by: i) identification of the vine-specific products based on the local guidelines for the vine-protection practices, ii) hazard classification of the vine-specific PPPs based on the CLP pictograms and statements (Classification, Labelling and Packaging Regulation, EC/1272/2008). This information, combined with the extension of the wine-growing areas from land use geographical data (Corine Land Cover 2018), allowed to outline, by assuming the use of the PPP in the municipality of sale, a map showing the hazard level of the wine-growing areas. The geospatial analysis based on the level of superimposition obtained between the extension of the wellhead protection areas and the wine-growing areas, led to a vulnerability map for wells. The map, resulting from the definition in different scenarios of the WHPAs extensions based on a geometrical criterion and the PPPs-based hazard of the vineyards, gives a clear picture of the wells that require PPPs-specific actions to minimize the risk for the quality of the water supplied for human consumption. 

Unconfined shallow aquifers are particularly exposed to the risk of contamination. Especially when exploited for drinking water production, for which water quality is of particular concern, careful monitoring of the physical processes and detailed characterization of the subsurface properties are crucial. Furthermore, the possible presence of heterogeneities, such as intricate networks of hydraulically conductive paleo-channels that are often inherent in alluvial aquifers, can establish preferential pathways. Consequently, monitoring activities in these complex environments pose serious challenges and raise the demand for advanced techniques and innovative approaches. In this context, recent advances have been made possible by employing Fiber Optics Distributed Temperature Sensing (FO-DTS). This technology combines the use of heat as a natural tracer with a detailed spatiotemporal resolution and has proven informative in a wide variety of applications. In this study, we applied downhole passive FO-DTS to a cluster of piezometers in a highly heterogeneous phreatic gravelly aquifer. The aquifer is exploited for irrigation and drinking water supply, and exhibits both natural and pumping-induced groundwater temperature fluctuations. Vertical transient water temperature profiles were acquired over a 1-month experiment. Borehole-dependent and depth-related features of the temperature measurements were ascribed to possible spatial structures having different hydraulic conductivity. The collected data were used to invert the three-dimensional saturated hydraulic conductivity field of a physics-based numerical model that couples flow and heat transport. Even without active heating, FO-DTS has demonstrated its ability to provide valuable insights at an unprecedentedly high resolution.