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For a reliable evaluation of the geo-environmental risk due to naturally occurring asbestos (NOA) during rock excavation of large infrastructure projects, a proper procedure is needed. First, it is necessary to provide a detailed geological model tailored to the NOA-related issues that should drive the rock sampling procedures in order to obtain a representative sampling. The sampling procedures should take into account lithological variability and relative spatial distributions of the rock units. The geological model for NOA should be thus constrained by the main NOA petrofacies occurring in a given geotectonic context, which take into consideration both the mineralogical and structural features, and the identification of NOA homogeneous zones in which the NOA petrofacies are distributed. In this paper, some geo-environmental problems faced during the excavation, in meta-ophiolites, of a long highway tunnel are described. The geological model of the complex setting of the tunnel area (northern Italy, Alps-Apennines junction) is described, focusing on how the NOA-related problems were addressed to allow reliable and detailed estimations of NOA contents for each NOA homogeneous zone and the relevant tunnel layout segment.

Realization of large geo-engineering projects in rocks containing naturally occurring asbestos (NOA) must address several crucial geo-environmental issues, including the design of the construction site, the enforcement of health protection measures and the environmentally responsible spoil management. This leads to a compelling need to develop effective and standard procedures to evaluate the distribution and concentration of NOA in rock volumes. NOA petrofacies are here proposed as an innovative tool to evaluate the asbestos distribution and concentration in complex geological settings. NOA petrofacies are fundamental asbestos-bearing rock types, consisting in recurrent lithological and structural features controlling asbestos occurrence. Here we describe and discuss how the NOA petrofacies approach was utilized in a geo-environmental study for the evaluation of asbestos content in a complex meta-ophiolite suite, which will be crossed by the “Gronda di Genova” highway by-pass project (Genoa, NW Italy). NOA petrofacies were used to predict the distribution and relative abundance of NOA in geologically homogeneous zones characterized by the occurrence of specific NOA minerals.