Application of geochemistral and isothopical analysis methods (87Sr/86Sr) in hydrogeological characterization of some springs in Simbruini mountains

This paper is part of a wider research program dealing with the application of the isothopic geochemistry to hydrogeological aims. In fact the use of this kind of isothopic analysis for a better comprehension of water chemistral evolution due to its interaction with the different type of geological formations during its path, is now well accepted from the scientific point of view. In particular in this paper we present the results of the application of a new method based on the Sr isothopical geochemistry. In this method the 87Sr/86Sr ratio is used as a process tracer related to other chemistral water elements, used as check tracers. Through this technique it is possible to give some more information about the groundwater flowing to the most important springs that now feed one of the largest civil water network of the neighbourhood of Rome. Both the values of the concentration of principal and secondary elements, and the 87Sr/86Sr isotopic ratio of water flowing out from Ceraso, Cesa degli Angeli, Pantano Alta, and Carpinetto springs have been found. The named springs present the largest debit coming out from the Simbruini Mountains aquifer. Ceraso spring is placed under Arcinazzo hill, while the others are near Simbrivio river, that flows in Aniene river on the rightside (Southern Lazio – Central Italy). The main chemistral properties of these waters come from the fact that they flow in the Simbruini-Ernici – M. Cairo carbonatic unit. They show the complex underground hydric circulation that takes place in these rocks. The geological importance of this unit comes from its being nord-west boarded by the regional Olevano-Antrodoco master fault. Its characteristic is that the carbonatic formation arises almost everywhere, except in Vallepietra-Filettino and Guarcino-Trisulti where a dolomitic basement arises. The carbonatic structure, and sometimes the dolomitic one, are actually important underground reservoirs. From these places water flows down to the general drainage axis of the area. That is represented by the Aniene valley. The waterflow is mainly due to a variable secondary permeability by fessuration improved by karstic processes, while the primary permeability, due to porosity, is very, very low. We have many hydrogeological studies dealing with these springs characterization, but only in the last past it has been started to analyse the geochemistral properties of the waters coming out from these springs. On the contrary the determination of the preferential groundwater paths is one of the most interesting aspects to know in the aim of protecting these waters. As the matter of fact we started to study the chemical evolution of these waters during their paths in this aquifer, and in this paper well present the results of the application of our method based on the analysis of the 87Sr/86Sr isotopic ratio, correlated to other chemical elements of these waters, in the aim of characterize their flow in the aquifer under study.