EVALUATION OF UNCERTAINTIES IN A 3-DIMENSIONAL GROUNDWATER CONTAMINATION PLUME

Geostatistical simulation and groundwater modeling are combined to estimate the probability of exceeding a threshold contamination level an aquifer. The analysis is completed in three dimensions with two sources of uncertainty considered: initial plume characterization, and aquifer parameter estimation. Initial plume location and intensity are based on a limited number of borehole measurements. Conditional simulation is used to generate possible plume configurations which provide initial conditions for a groundwater model. Simultaneously, aquifer parameters are also simulated, and repeated running of the groundwater model provides a frequency distribution of contaminant level at a selected compliance surface and future time. The method has been tested at a low-level radioactive waste reprocessing facility. Numerical results show that the effect of uncertain initial plume characterization may have a larger impact on the modeling process than the effect of uncertain aquifer parameters. Both effects should be considered in order to evaluate the need for additional aquifer remediation efforts.