Vulnerability assessment of karst aquifers using the COPA+K index based method: the case of the Valseriana springs (Northern Italy)

The Valseriana is a Pre-Alps valley located in the province of Bergamo (Northern Italy). It is characterized by high water availability due to the combination of its karst environment and a high average precipitation rate (2000 mm/year). Therefore, its main springs (Nossana and Ponte del Costone) assume a strategic importance for the water domestic service of the city of Bergamo and other municipalities in the area. Proper management oriented to the preservation of these water systems is crucial. Intrinsic vulnerability maps are currently one of the most valuable tools for assessing the pollution sensitivity of an area. Index-based methods allow its assessment even in cases where large amounts of data are not available and without requiring intense computational effort. The study aimed to evaluate and improve index-based approaches to assess intrinsic vulnerability including the specific characteristics of the Pre-Alps region. First, the classical methods for karst environments were applied (COP and EPIK) using GIS software. These evaluation techniques did not allow to underline the different behavior of the two springs (dominant drainage system Nossana, dispersive system Ponte del Costone). Therefore, the COP method was extended in the COPA+K approach by adding two further factors. In detail, the influence of major discontinuities on the water system according to their distance from the spring (A factor) and the development of the karst network (K factor) were considered. The statistical analysis of the results revealed the advantages of using this new method in this area compared with COP and EPIK. COPA+K allowed a greater detail in the identification of the most vulnerable areas (from 35.6% to 23.6% considering the whole area) and the percentage difference between the most vulnerable areas of Nossana and Ponte del Costone increased from 5.2% to 17.5%.