Probabilistic cost-benefit analysis for mitigating hydrogeological risks in underground construction

Leakage of groundwater into underground facilities can subsequently cause groundwater drawdown, subsidence and subsidence damages to the built-up environment. In order to reduce the risk of damage, measures to mitigate the risks must often be implemented. The aim of this paper is to describe and demonstrate a probabilistic cost-benefit analysis approach to assess the economic profitability of investing in different risk mitigation alternatives. Since underground construction is always associated with uncertainties, the analysis uses probability distribution functions for uncertain parameters and Monte Carlo simulations to quantify probabilities of damage and implementation costs. The proposed approach is exemplified with a case study, the road tunnel project Bypass (F\uf6rbifart) Stockholm in eastern Sweden, for which four risk mitigation alternatives were evaluated. In conclusion, the approach helps to highlight the economic effects of different risk mitigation approaches and constitute a transparent support for decisions on implementation of risk mitigation. For the case study, the analysis indicates that the implementation costs of ∼ 7000 MSEK (700 million EUR) for risk mitigation needed to fulfil the legal requirements, from the Swedish Land- and Environmental court, in the form of ambitious sealing strategies are disproportionate relative to the benefits of ∼ 50 MSEK (5 million EUR) gained in the form of reduced damage risk for the built-up environment. In other words, billions SEK of taxpayers\u27 money are spent on unnecessary expenses to fulfill legal requirements without societal benefits. The novelty of the paper constitutes the coupling of models and combination of established methods for management of hydrogeological risks

A Framework for Risk-Based Cost-Benefit Analysis for Decision Support on Hydrogeological Risks in Underground Construction

Construction below the ground surface and underneath the groundwater table is often associated with groundwater leakage and drawdowns in the surroundings which subsequently can result in a wide variety of risks. To avoid groundwater drawdown-associated damages, risk-reducing measures must often be implemented. Due to the hydrogeological system\u27s inherent variability and our incomplete knowledge of its conditions, the effects of risk-reducing measures cannot be fully known in advance and decisions must inevitably be made under uncertainty. When implementing risk-reducing measures there is always a trade-off between the measures\u27 benefits (reduced risk) and investment costs which needs to be balanced. In this paper, we present a framework for decision support on measures to mitigate hydrogeological risks in underground construction. The framework is developed in accordance with the guidelines from the International Standardization Organization (ISO) and comprises a full risk-management framework with focus on risk analysis and risk evaluation. Cost-benefit analysis (CBA) facilitates monetization of consequences and economic evaluation of risk mitigation. The framework includes probabilistic risk estimation of the entire cause-effect chain from groundwater leakage to the consequences of damage where expert elicitation is combined with data-driven and process-based methods, allowing for continuous updating when new knowledge is obtained

Framework for Risk-Based Decision Support on Infiltration and Inflow to Wastewater Systems

Infiltration and inflow (I/I) to wastewater systems cause e.g., flooding, pollution, and the unnecessary use of the limited resources in society. Due to climate change and an increased need for the renewal of piping systems, making the right decisions on how to handle I/I is more important than ever. This paper presents a novel framework for risk-based decision support on I/I based on established theories on risk assessment and decision-making. The framework is presented on a general level and suggests that uncertainties are included in the decision-making process, together with criteria representing the economic, social, and environmental dimensions of sustainability. Published models on I/I and decision support are evaluated based on criteria from the framework showing that (1) the models rarely include risk-based decision-making or uncertainties in the analyses and that (2) most models only include project-internal financial aspects, excluding social and environmental, as well as project-external aspects, of I/I and I/I measures. A need for further research to develop a more holistic decision support model for I/I is identified, and it is concluded that the application of the proposed framework can contribute to more sustainable decisions on how to handle I/I and provide transparency to the process

Accounting for Unexpected Risk Events in Drinking Water Systems

Unexpected risk events in drinking water systems, such as heavy rain or manure spill accidents, can cause waterborne outbreaks of gastrointestinal disease. Using a scenario-based approach, these unexpected risk events were included in a risk-based decision model aimed at evaluating risk reduction alternatives. The decision model combined quantitative microbial risk assessment and cost–benefit analysis and investigated four risk reduction alternatives. Two drinking water systems were compared using the same set of risk reduction alternatives to illustrate the effect of unexpected risk events. The first drinking water system had a high pathogen base load and a high pathogen log10 reduction in the treatment plant, whereas the second drinking water system had a low pathogen base load and a low pathogen Log10 reduction in the treatment plant. Four risk reduction alternatives were evaluated on their social profitability: (A1) installation of pumps and back-up power supply, to remove combined sewer overflows; (A2) installation of UV treatment in the drinking water treatment plant; (A3) connection of 25% of the OWTSs in the catchment area to the WWTP; and (A4) a combination of A1–A3. Including the unexpected risk events changed the probability of a positive net present value for the analysed alternatives in the decision model and the alternative that is likely to have the highest net present value. The magnitude of the effect of unexpected risk events is dependent on the local preconditions in the drinking water system. For the first drinking water system, the unexpected risk events increase risk to a lesser extent compared to the second drinking water system. The main conclusion was that it is important to include unexpected risk events in decision models for evaluating microbial risk reduction, especially in a drinking water system with a low base load and a low pathogen log10 reduction in the drinking water treatment plant

Risk-based cost-benefit analysis for evaluating microbial risk mitigation in a drinking water system

Waterborne outbreaks of gastrointestinal diseases can cause large costs to society. Risk management needs to be holistic and transparent in order to reduce these risks in an effective manner. Microbial risk mitigation measures in a drinking water system were investigated using a novel approach combining probabilistic risk assessment and cost-benefit analysis. Lake Vomb in Sweden was used to exemplify and illustrate the risk-based decision model. Four mitigation alternatives were compared, where the first three alternatives, A1-A3, represented connecting 25, 50 and 75%, respectively, of on-site wastewater treatment systems in the catchment to the municipal wastewater treatment plant. The fourth alternative, A4, represented installing a UV-disinfection unit in the drinking water treatment plant. Quantitative microbial risk assessment was used to estimate the positive health effects in terms of quality adjusted life years (QALYs), resulting from the four mitigation alternatives. The health benefits were monetised using a unit cost per QALY. For each mitigation alternative, the net present value of health and environmental benefits and investment, maintenance and running costs was calculated. The results showed that only A4 can reduce the risk (probability of infection) below the World Health Organization guidelines of 10−4 infections per person per year (looking at the 95th percentile). Furthermore, all alternatives resulted in a negative net present value. However, the net present value would be positive (looking at the 50th percentile using a 1% discount rate) if non-monetised benefits (e.g. increased property value divided evenly over the studied time horizon and reduced microbial risks posed to animals), estimated at 800–1200 SEK (€100–150) per connected on-site wastewater treatment system per year, were included. This risk-based decision model creates a robust and transparent decision support tool. It is flexible enough to be tailored and applied to local settings of drinking water systems. The model provides a clear and holistic structure for decisions related to microbial risk mitigation. To improve the decision model, we suggest to further develop the valuation and monetisation of health effects and to refine the propagation of uncertainties and variabilities between the included methods

Economic Valuation for Cost–Benefit Analysis of Health Risk Reduction in Drinking Water Systems

Microbial risk mitigation measures in drinking water systems aiming at preventing gastrointestinal disease can provide substantial societal health benefits if implemented properly. However, the procedure of including and monetising the health benefits in cost–benefit analysis (CBA) has been somewhat scattered and inconsistent in the literature, and there is a need for a comparison of available methods. First, through a literature review, we identified the methods to include health benefits in decision support and to monetise these benefits in CBA. Second, we applied the identified health valuation methods in a case study. In the case study, we investigated if changing the health valuation method could change the rank order of the decision alternatives’ net present values. In the case study a risk-based decision model that combined quantitative microbial risk assessment and CBA was used. Seven health valuation methods were identified, each of them including different aspects of health benefits. The results of the case study showed that the choice of the health valuation method can change the rank order of decision alternatives with respect to their net present values. These results highlight the importance of choosing an appropriate health valuation method for the specific application. Although this study focused on the drinking water context, the identified health valuation methods can be applied in any decision support context, provided that input in terms of the health risk reduction is available

Dynamic Water Balance Modelling for Risk Assessment and Decision Support on MAR Potential in Botswana

Botswana experiences a water stressed situation due to the climate and a continuously increasing water demand. Managed Aquifer Recharge (MAR) is considered, among other measures, to improve the situation. To evaluate the possibility for increased water supply security, a probabilistic and dynamic water supply security model was developed. Statistically generated time series of source water availability are used in combination with the dynamic storages in dams and aquifers, and the possible supply is compared with the demand to simulate the magnitude and probability of water supply shortages. The model simulates the system and possible mitigation measures from 2013 to 2035 (23 years), using one-month time steps. The original system is not able to meet the demand, and the estimated volumetric supply reliability in the year 2035 is 0.51. An additional surface water dam (now implemented) will increase the reliability to 0.88 but there will still be a significant water shortage problem. Implementing large-scale MAR can further improve the reliability to at least 0.95. System properties limiting the effect of MAR are identified using the model and show how to further improve the effect of MAR. The case study results illustrate the importance and benefit of using an integrated approach, including time-dependence and future scenarios, when evaluating the need and potential of MAR

VRAKA—A Probabilistic Risk Assessment Method for Potentially Polluting Shipwrecks

Shipwrecks around the world contain unknown volumes of hazardous substances which, if discharged, could harm the marine environment. Shipwrecks can deteriorate for a number of reasons, including corrosion and physical impact from trawling and other activities, and the probability of a leakage increases with time. Before deciding on possible mitigation measures, there are currently few comprehensive methods for assessing shipwrecks with respect to pollution risks. A holistic method for estimating environmental risks from shipwrecks should be based on well-established risk assessment methods and should take into account both the probability of discharge and the potential consequences. The purpose of this study was therefore to present a holistic risk assessment method for potentially polluting shipwrecks. The focus is set to developing a method for estimating the environmental consequences of potential discharges of hazardous substances from shipwrecks and to combine this with earlier research on a tool for estimating the probability of discharge of hazardous substances. Risk evaluation should also be included in a full risk assessment and is the subject of further research. The consequence assessment was developed for application in three tiers. In Tier 1, the probability of discharge and possible amount of discharge are compared to other shipwrecks. In Tier 2, a risk matrix, including a classification of potential consequences, is suggested as a basis for assessment and comparison. The most detailed level, Tier 3, is based on advanced tools for oil spill trajectory modeling and sensitivity mapping of the Swedish coast. To illustrate the method an example application on two wrecks is presented. Wreck number 1 present a lower probability of discharge and a lower consequence in a Tier 1 and Tier 3 assessment. For the Tier 2 consequence assessment, the two example wrecks present equal consequence. The tool for estimating the probability of discharge of hazardous substances from shipwrecks, and the approach for consequence estimation, offers a comprehensive method for assessing the risks presented by potentially polluting shipwrecks. The method is known as VRAKA (short for shipwreck risk assessment in Swedish) and provides decision support, facilitating prioritization of risk mitigation measures enabling efficient use of available resources

Cost to society from infiltration and inflow to wastewater systems

Water from infiltration and inflow to wastewater systems is an extensive problem causing costs to society in various ways. Comprehensive methods for supporting decisions on how to efficiently mitigate the problems in a sustainable manner are, however, missing today. This paper presents a novel risk-based model to assess the cost to society from infiltration and inflow to wastewater systems by monetising effects related to treatment of wastewater, pumping, combined sewer overflows, and basement flooding. The present value is calculated for a specified time horizon and discount rate, using a cost-benefit analysis approach. To acknowledge the various uncertainties, a probabilistic approach is applied where probability distributions represent the input variables. The model is shown to be applicable by illustrating its use in a case study area in Gothenburg, Sweden. Main results from the case study show that most of the costs are related to investments at the wastewater treatment plant and restoration due to basement flooding events. Sensitivity analyses show that the result is highly dependent on factors such as the volume of infiltration and inflow water, the share of basement flooding, and the discount rate. Using expert elicitation to quantify input data is also illustrated and shown to be a valuable method. The presented model fills an important research knowledge gap and will facilitate a more sustainable and comprehensive handling of water from infiltration and inflow