Estimating the remediation costs following an accident

The number of accidents involving extended pollution of environmental matrixes is increasing, as well as the public concern. The responsible is charged for remediation costs, which will depend on amount and type of affected environmental matrixes, and on their respective pollution level. Generally, the costs are established at the end of a criminal trial, based on technical expert surveys (of the Public Prosecutor, of the Judge, of the Defense) which, usually, reach rather different conclusions. The amount of polluted matrix should be estimated comparing the amount of individual substances spilled in the matrix to their maximum allowable concentration: in some cases, it is simply calculated dividing the amount of spilled substance by its limit thresholds. This will result in a huge amount of contaminated matrix, but at rather low pollutant concentration. On the contrary, the pollutant will disperse within the matrix, establishing concentration profiles, and the amount of polluted matrix should be that where the concentration is above the limit threshold. The amount of polluted matrix will be much smaller than that estimated with the simplistic criterion, but the average concentration of pollutant will be higher. The choice of the remediation process, will strongly depend on the used approach, together with the time to complete remediation, which affects the size of the plant and its cost. This work shows the results of a study case concerning a pollution of surface water, deriving from the explosion of a tank in a TDI production unit occurred at Mestre (Italy) in 2002