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(21-15) Uncertainty and global sensitivity analyses for risk based remediation of contaminated sites. Carlon, Claudio*,2, Nadal, Nadia2, Critto, Andrea1, Marcomini, Antonio1, 2 Consorzio Venezia Ricerche, Via della Libertà 5/12, Venice, Italy1 University of Venice, Department of Environmental Sciences, Calle Larga S. Marta 2137, Venice, Italy ABSTRACT- The Risk Assessment applied to contaminated sites is a technical procedure to determine site specific cleanup goals. This procedure starts with a numerical definition of acceptable risk for human health and works back to the level of contamination that will produce an acceptable risk level. The American Society for Testing and Materials proposed a three tiered risk assessment procedure which requires increasingly site-specific data, more expensive and time consuming analysis, moving from the first to the third tier level. In this work, the tiered analysis is applied to three case studies to verify how risk-based clean-up goals depend upon site-specific characteristics and to outline advantages and limits of a more accurate probabilistic risk analysis. The second and third tier levels were performed by applying the Risk Based Corrective Action Tool Kit ©(Groundwater Service Inc., 1995) and the American Petroleum Decision Support System© (API, 1993) algorithms, respectively. The probabilistic risk analysis was implemented by a Monte Carlo simulation aiming at characterising the uncertainty of the outputs as result of the uncertainty of the model inputs. The acceptable risk for human health resulting from the deterministic analysis of the risk assessment turned out to be not acceptable after undertaking the uncertainty analysis. The use of deterministic third tier only, without uncertainty analysis, provided site specific cleanup goals that are not protective for the human health. It is recommended, in this case, to close the risk analysis at the second tier, keeping a conservative estimation for both risk and cleanup goals. Furthermore, a global sensitivity analysis was undertaken. The sensitivity technique employed is the Morris screening method included in the SIMLAB software© (JRC-ISIS, 1999). The application of the global sensitivity analysis allowed to determine the input parameters that exhibit most influence on probabilistic risk estimation and to identify the parameters requiring a deeper characterisation. Key words: Probabilistic Risk Assessment, Contaminated sites, Sensitivity Analysis, Monte Carlo Analysis |
