The new high-speed, high-capacity Treviglio-Brescia railway line is an integral part of the Trans-European Transport Network, the “Mediterranean Corridor,” and constitutes a critical stage in the construction of the high-speed, high-capacity Milan-Verona railway line, which extends a total of 140 km, 27 km of which have been in operation between Milan and Treviglio since 2007. The activities currently under way include the construction of a railway line covering a distance of ~52 km between Treviglio and Brescia, and the completion of a series of complementary projects to mitigate the interference with other infrastructures (e.g., canals, underground utilities) and new road systems. Geological investigations have been necessary during the course of the work, to manage excavations and excavated materials, to manage abandoned waste encountered along the line, and for remediation of contaminated sites. In addition to the characterization of the project area, data collected have contributed to the Environmental Monitoring Plan issued by the Consorzio Eni per l’Alta Velocità (CEPAV Due), which will monitor for potential environmental impacts caused by the execution of the project, particularly related to the soil, surface water, and groundwater, and the project measures needed to reduce environmental impact. This paper provides an overview of the activities carried out so far, as illustrated with some case studies.