A Mass Balance-Based 1D Mass Transport Model

Groundwater remedial design typically requires the development of a reliable mass transport model to evaluate clean up alternatives. A major challenge in the development of a mass transport model is the identification of source release terms such as location and time of release. Although the source location may be characterized during site investigations, the time terms are unknown or poorly known at many sites. This study uses a mass balance-based approach to explicitly account for uncertainty in rectangular pulse release time variables instead of using inverse techniques to rigorously define the release history. The mass balance approach relies on the collection of groundwater concentration data and the standard assumptions used to develop one-dimensional solutions to the advection dispersion equation. A spreadsheet model has been developed to accommodate Monte Carlo simulations, and a concentration dataset from a Nebraska Superfund site was used to evaluate the model. Reasonable results were achieved when the source time parameters were assumed to be random, and the results improved when the mass of contaminant in the aquifer was also assumed to be random.