Back-Calculation of Soil Cleanup Levels Utilizing Monte Carlo Techniques. R. J. Fares and K. G. Symms, Environmental Standards, Inc., Sterling, VA, and Valley Forge, PA
The debate continues regarding the applicability of Monte Carlo analysis to back-calculate soil cleanup levels at contaminated sites. Cleanup levels generally are calculated using inverted deterministic risk equations. It has been argued that when variability is introduced, those equations no longer follow the rules of ordinary algebra, and may result in estimates of cleanup target values that are not protective. One recommended solution is a process called deconvolution, which if applied correctly, reduces uncertainty by yielding a distribution with smaller weights in the tails. One problem with using deconvolution however is that many of the techniques are numerically unstable and difficult to execute, thereby making them impractical for routine risk analyses. This paper will show that there are situations in which Monte Carlo is not only applicable, but appropriate for back-calculating soil cleanup levels. A process is described using data from a former Manufactured Gas Production (MGP) site as an example, to demonstrate the relative ease with which credible, protective soil cleanup levels can be developed in appropriate situations.
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