Analysis of the Recharge Area of the Perrot Spring (Aosta Valley) Using a Hydrochemical and Isotopic Approach

Abstract

The Perrot Spring (1300 m a.s.l.), located to the right of the Chalamy valley in the Monte Avic Natural Park (Valle d’Aosta, Italy), is an important source of drinking water for the municipality of Champdepraz. This spring is located on a large slope characterised by the presence of a Quaternary cover of various origins (glacial, glaciolacustrine, and landslide) above the bedrock (essentially serpentinite referred to the Zermatt–Saas Zone, Penninic Domain). Water emerges at the contact between the landslide bodies and impermeable or semi-permeable glaciolacustrine deposits. The aim of this study is to define the processes and recharge zones of this spring. The analysis of the data revealed the presence of two contributions to the Perrot Spring input: a spring thaw contribution defined by a small increase in flow and an autumn contribution from rainwater infiltration. The low average temperature and low variation of the annual temperature (4.8–6.5 °C) suggest a sufficiently deep flow circuit. Chemical analyses showed a groundwater chemistry consistent with the regional geology: the hydrochemical facies is calcium–magnesium bicarbonate and isotopic analyses (δ2H and δ18O) of rainfall and spring water suggested a recharge altitude of about 2100 m a.s.l. In conclusion, this study makes it possible to recognize the water inputs to the spring discharge and to delineate its recharge area, which can be proposed to implement strategies to protect the resource.