Abstract

This article describes the applications of a commonly used groundwater mixing model in conjunction with a one-dimensional vadose zone transport model, VLEACH, to predict the impact of residual soil concentrations of methyl tertiary butyl ether (MTBE) on groundwater quality at a site located in Los Angeles, California, U.S.A. An appropriate soil remedial concentration determined to be protective of groundwater quality is developed based on transport model results. Monte Carlo Simulation (MCS) is conducted for the groundwater mixing model. Based on MCS results, a soil remedial concentration is calculated in relation to a probabilistic confidence level. The resultant MTBE soil remedial concentration ranges from 35 μg/kg at a 90% confidence level to 69 μg/kg at a 50% confidence level in terms of protecting groundwater quality. The results of this study clearly demonstrate that model predictions combined with a probabilistic approach by MCS can provide better information to decision makers than conventional model predictions using single-point average input values. The methodology presented in this article can be useful to other regulatory decision-making processes that have similar situations in determination of soil remedial concentrations.