Target cleanup levels at the site of a former manufactured gas plant in Northern Italy: Deterministic versus probabilistic results

Abstract

A quantitative analysis of allowable soil concentrations using deterministic and probabilistic risk analysis methods was carried out for a large and heavily contaminated industrial site where remediation costs to meet soil standards (not risk-based) issued by the regulatory agency were higher than the commercial value of the site. Deterministic cleanup targets, based on a risk-based corrective action procedure, allow a 5-fold reduction in the volume of soil to be decontaminated. The site-specific, probabilistic analysis shows that the deterministic cleanup standards for volatile organic compounds were lower than those required to meet the probabilistic criteria but were higher, and thus less conservative, for polycyclic aromatic hydrocarbons and inorganic substances. The probabilistic methods used show that deterministic standards may hide significantly different levels of conservatism in relation to the uncertainty and variability present in each exposure parameter. The expediency of probabilistic calculation to avoid over-remediation efforts is not certain as probabilistic results may be more stringent than deterministic ones; therefore, remediation costs are related not only to the allowable concentrations of single species but also to the mix of contaminants found on a specific site.