QUANTIFICATION OF UNCERTAINTY IN EXPOSURE ASSESSMENTS AT HAZARDOUS-WASTE SITES

Many of the risk assessment approaches being applied at hazardous waste sites fail to adequately account for the ground-water flow and solute transport processes (and their uncertainties) that move the contaminant from the source to the receptor. For example, one recommended model assumes the contaminant concentration at the source is equal to the contaminant concentration at the receptor. A more realistic way to estimate receptor concentrations for risk assessment would be to use technically accepted ground-water flow equations coupled with the advection-dispersion equation and use Monte Carlo techniques to address parameter uncertainty. A complex numerical model and a simple analytical model were used to simulate ground-water flow and solute transport from a hypothetical waste site to a subsurface drain using both small and larger scale hydraulic properties. Results indicate that the predicted receptor concentration is considerably lower than the source concentration when knowledge of the local hydrogeology is considered in the transport simulations.