PROBABILISTIC SOIL CONTAMINATION EXPOSURE ASSESSMENT PROCEDURES

A comparison is conducted between Monte Carlo simulation and firstorder uncertainty analysis within the framework of an exposure assessment procedure. The modeled scenario consists of contaminated soil located directly above an aquifer and upgradient of a water supply well. For the exposure assessment procedure, the exposure point concentration is predicted by performing Monte Carlo simulation using a one-dimensional vertical, soil-water solute-transport model coupled with a two-dimensional, horizontal ground-water fate and transport model. The result is expressed as a probability distribution of the contaminant concentration at the point of human exposure (water supply well). To complete the exposure assessment procedure, the concentration corresponding to a prespecified risk level (usually 5%) is evaluated against the appropriate and/or relevant health-based standards for the site. First-order uncertainty analysis is another probabilistic method that under certain circumstances may be applied in place of Monte Carlo simulation. For the hypothetical site modeled in this research, first-order uncertainty analysis was found to be a useful tool for examining the relative importance of the various site parameters, although the method was not found to be a substitute for Monte Carlo simulation in the context of this particular exposure assessment procedure.© ASCE.