Identification of benefits and costs from the reduction of hydrogeological risks in underground construction

Implementing measures to reduce hydrogeological risks from underground construction below the groundwater table is often expensive. Cost-benefit analysis (CBA) assesses whether measures give a positive societal net benefit and thereby indicates how society’s limited resources can be used efficiently. For a CBA to be valid, all costs and benefits for all affected stakeholders should be included. This implies that a thorough and comprehensive identification of cost and benefit items is the crucial basis for the development of a CBA. In this paper, a novel and comprehensive approach for identifying benefit and cost items of implementing hydrogeological risk-mitigation measures is presented for application in underground construction. The novelty lies in the procedure of integrating hydrogeological knowledge of common underground type settings with the cascade model—a well-established framework for linking natural, social, and economic systems (Haines-Young and Potschin-Young, 2018)—and categorizing leakage-induced risks, and thereby the potential benefits of mitigating these risks have been systematically identified. Relevant groundwater leakage-induced cascades are presented in a general format, together with examples from the literature for providing a user-friendly tool for risk identification that considers the whole chain of events from groundwater impact to social and economic consequences. The combination of using the basis of the cascade model together with international literature results in a general method that is applicable across various hydrogeological settings. The generic arrangement of the presented cascades also enables application as new construction technologies emerge since the initiation of a cascade is not fixed to a certain technology but rather to the effects on the groundwater conditions from the construction activity. An identification of cost and benefit items in two railway tunnel projects in Sweden is also presented as a qualitative CBA to demonstrate the usability of the risk cascades as a basis for identification of items to subsequently be monetized in a quantitative CBA. Finally, the paper discusses the upcoming steps, challenges, and strategies to handle them, associated with obtaining a complete quantitative CBA.