ASSESSING GROUNDWATER VULNERABILITY USING A DILUTION FACTOR APPROACH

Three-dimensional subsurface simulation modeling of contaminant transport at regional scales can require prohibitively costly computational efforts. Although two-dimensional contaminant transport simulations can be used to assess groundwater vulnerability, these assessments are biased by higher concentrations than those predicted by three-dimensional simulations. In this work, a dilution factor approach is proposed to predict peak concentrations for a three-dimensional domain based on two-dimensional simulation results. Using analytical solutions, the concentration relation between two- and three-dimensional solutions are first elucidated for solute transport in uniform porous media with steady-state two- and three-dimensional flow. Dilution factors are then developed with the aid of simulated breakthrough curves from data sets at the Hanford site in southeastern Washington state. Comparisons of the dilution factor approach and three-dimensional solute transport simulations show that the dilution factors perform well with respect to mass balance, concentration magnitude, and the timing of concentration peaks. Although practical limitations exist on the application of the dilution factor, this approach greatly reduces the computational cost associated with large-scale simulations while providing realistic predictions of peak concentrations and arrival times.