<p>The extent and the fluid dynamics of the vadose zone (VZ) of an aquifer have a direct impact on the aquifer recharge, the water quality and the pollutants transfer from the soil to the groundwater. The water – rock interactions and mass and heat transfers under the impact of microbial processes and agricultural practices could undergoes significant changes in the chemical composition of the water flowing throughout the VZ, which may induce pollution of groundwater.</p><p>The growing dependence on groundwater for potable water supplies draws attention to protect the quality of groundwater resources at national and international levels to the need. It is important to detect the contamination risk of aquifers and develop an integrated water management methodology based on innovative environmental monitoring tools and sophisticated numerical models to protect groundwater resources and guarantee their good quality for domestic, agricultural and industrial needs. For this reason, the monitoring of VZ dynamics has become essential to study the transfer mechanisms of mass (water, gas and contaminants) and heat from the soil to the groundwater. This should allow rapid detection of the pollutants migration through an aquifer and take relevant measures to protect groundwater before the contaminants reach the water table.</p><p>In this context, an Observatory of transfers in the vadose zone (O-ZNS) is being developed at Villamblain (Orléans, France) in an agricultural field. The O-ZNS project consists of a well with a diameter of 4 m and a depth of 20 m which will allow access to the entire VZ of the Beauce aquifer. The main target of the O-ZNS platform is to acquire original and unique data on the reactive transfers of fluids and heat in the VZ, in order to follow in situ and in real time the highly coupled physical, chemical, and biological processes taking place over the long term. The O-ZNS project also aims to assess the performance of all types of instrumentation dedicated to non-destructive measurement or local sampling of fluids, rocks, and microbs in the VZ for long duration.</p><p>To meet these objectives, a myriad of innovative monitoring tools (e.g.,environmental sensors, fiber optic sensors, geophysical imaging, ….) will be deployed in the O-ZNS from the soil surface to the aquifer (from 0 to 20 m deep) using the well and the surrounding boreholes. Also, note that to date, there are still difficulties in the instrumentation of rock materials and relevant solutions must be developed. These environmental monitoring techniques will allow to generate a huge quantity of data on the physical, chemical, and microbiological coupled processes.</p>

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<div> <p>The Observatory of the Vadose Zone (OZNS) is addressing the role of the unsaturated zone in the transfers of water, heat, and pollutant, between the soil and the aquifer. This project implements a unique observatory within the Beauce Limestone Formation at Villamblain (France). This observatory consists of a large central well (20 m deep and with a diameter of 6.1 m) surrounded by satellite drill holes and surface installations within an area with a radius of a few tens of meters. The overall observatory spans from the surface down to 25 m depth, reaching the aquifer and the barrier layer of the Molasses du Gâtinais. The instrumented surface, central well, and satellite drill holes will produce decade-long records of the vadose zone to evaluate its impact on water and pollutant transfers, while monitoring its long-term evolution in a context of climate change.</p> </div> <p> </p> <p>The large central well is primarily designed for easily installing, maintaining, and testing geophysical and hydrological sensors over the lifetime of the observatory, but it also provides a unique chance to observe the complex structuration of the vadose zone and its host. In particular, the scale and configurations of the site provide a unique view of these rocks. They are made accessible at a micro-to-decametric scale, which extends drill core observations, and provide a nearly 3D view. This is interesting by comparison with typical outcrops at that scale (e.g., quarries), which are mostly 2D. Preliminary observations, from surrounding drill cores, revealed a particularly complex limestone formation, which consists of a series of terrestrial limestones, with palustrine and lacustrine facies and breccias, affected by a long history of fractures and alterations, silicification, and karstification. A very detailed characterisation of these facies thus requires to provide a high-resolution context for the various measurements and simulations of the transfers in the vadose zone.</p> <p>This contribution presents the construction of the numerical architecture and the acquisition process implemented for accommodating the very restricted access to direct observations during the construction of the well, which encompasses laser scanning (lidar) and high-resolution photogrammetry. The implications of the different acquisition protocols implemented during the process are discussed in terms of impacts on resolution, coverage, and spatial accuracy. The scanning was performed through 14 distinct stages, where only around 1.5 m height was accessible each time. One of the challenges was thus to stitch the different model rings into a common model. In the end, a complete model of the well surface was recorded with an average resolution of 3 pixels per millimetre.</p>