ESTIMATING THE PROBABILITY OF EXCEEDING GROUNDWATER QUALITY STANDARDS

A model for estimating the probability of exceeding groundwater qualit y standards at environmental receptors based on a simple contaminant t ransport model is described. The model is intended for locations where knowledge about site-specific hydrogeologic conditions is limited. An efficient implementation methodology using numerical Monte Carlo simu lation is presented. The uncertainty in the contaminant transport syst em due to uncertainty in the hydraulic conductivity is directly calcul ated in the Monte Carlo simulations. Numerous variations of the determ inistic parameters of the model provide an indication of the change in exceedance probability with change in parameter value. The results of these variations for a generic example are presented in a concise gra phical form which provides insight into the topology of the exceedance probability surface. This surface can be used to assess the impact of the various parameters on exceedance probability.