Tridimensional vulnerability assessment of wells supplying drinking water in agricultural areas

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).