## 5 Conclusions  
This research aims to define a model that can guide the financial operator to provide a judgement on the investment risk acceptability of civil projects. The idea is to define a new methodology for estimating project risk acceptability and tolerability thresholds that together uses the As Low As Reasonably Practicable (ALARP) logic, the Capital Asset Pricing Model (CAPM), and statistical survey methods. From the ALARP logic derives the concepts of risk acceptability and tolerability threshold, respectively the limit value \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Variable** & **Value** & **Variable** & **Value** & **Source** \\ \hline \(ke_{t}\) & 56.00\% & ke\({}_{a}\) & 60.00\% & Damodaran, 2020; Orbis database \\ \(re_{t}\) & 10.61\% & re\({}_{a}\) & 13.21\% & (see Table 1) \\ \(ke_{t}\) & 44.00\% & ke\({}_{a}\) & 40.00\% & Damodaran, 2020; Orbis database \\ \(r_{f}^{\prime}\) & 2.31\% & \(r_{f}\) & 2.31\% & (see Table 1) \\ ADF & 1.22\% & ADF & 1.22\% & Damodaran, 2020 \\ \(rd_{t}\) & 3.53\% & rd\({}_{t}\) & 3.53\% & - \\ \(t\) & 22.62\% & \(t\) & 22.62\% & Damodaran, 2020 \\ \hline WACC\({}_{t}\) & 7.25\% & WACC\({}_{a}\) & 9.15\% & Formulas (12) and (13) \\ \hline EIR\({}_{\xi}\) & 0.20\% & EIR\({}_{\xi}\) & 1.50\% & Damodaran, 2020 \\ \hline WACC\({}_{t}\) & 5.88\% &
\begin{tabular}{c} WACC\({}_{a}\) \\ (Euros) \\ \end{tabular} & 7.75\% & Formulas (17) and (18) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: WACC\({}_{t}\) and WACC\({}_{a}\) for Europe. below which the risk is broadly acceptable and that above which the risk is unacceptable to the analyst. The CAPM, on the other hand, exemplifies the theoretical reference for the estimation of acceptable and tolerable return values. In fact, this method makes it possible to estimate the risk-adjusted discount rate \(r(\beta)\), the minimum return expected from an investment project with risk profile \(\beta\)[46]. Statistical survey methods make it possible to calibrate risk acceptance thresholds for investments in a specific sector. This is done based on the systematic risk expressed by the \(\beta\) coefficient of a statistically acceptable panel of firms operating in a certain territorial context. Specifically, we define as tolerable as ALARP an investment whose return is equal to the return expected from a project with an average risk profile, i.e., one that is representative of the civil enterprises operating in a given territorial context. We then assume as widely acceptable to the investor an initiative whose average return is at least equal to the return expected from a project with a high-risk profile, i.e., representative of the first quartile of civil enterprises, i.e., those with lower returns and consequently riskier. The methodology defined for estimating the acceptable and tolerable risk-adjusted discount rate is an integral part of the model for analyzing, assessing, estimating, and treating risk and residual risk, i.e., that which remains despite the planned mitigation actions. In fact, the comparison between the expected return E(IRR) of a civil project--derived from the probability curve of the financial performance indicator--and the limit values of acceptable and tolerable risk-adjusted discount rate provides the economic operator with a more immediate and consistent assessment of the triangular balance of risks, costs, and benefits, also making the decision-making process more rational and transparent. The implementation of the model, tested with reference to listed European civil companies, leads to the following results. The investment risk can be considered: (i) widely acceptable for the economic operator if the expected internal rate of return E(IRR) is above 7.8%; (ii) unacceptable if the E(IRR) is below 5.6%; (iii) tolerable as an ALARP if the expected rate is between 5.6% and 7.8%. This means that in the latter case the risk of failure can be considered tolerable if further risk mitigation costs are disproportionate to the benefits to be achieved.