Geogenic versus Anthropogenic: Hydrocarbons in the Spoil from the Falkenstein and Spering Tunnels (A9 Pyhrn Autobahn, Austria)

Abstract

In the Falkenstein und Spering tunnels (A9 Pyhrn Autobahn; Northern Calcareous Alps), hydrocarbon contents (HC Index) in excess of the permitted threshold values were detected in the course of the routine statutory analysis of the excavated material. Comparative detailed geochemical analysis of retained reference samples, operational consumables and core samples from boreholes drilled into the tunnel wall show that threshold values of HC indices in the Reifling Limestone are exceeded due to the presence of locally generated natural hydrocarbons. The hydrocarbons were probably formed in marly zones of the carbonate rocks and migrated into the well‐developed fracture network. These hydrocarbons are characterized by high contents of n‐alkanes, high Ts/(Ts+Tm) ratios, a predominance of C27 and C29 steranes, and the lack of oleanane. Traces of hydrocarbons in the Wetterstein Limestone contain oleanane due to contamination by operating consumables.