Dupuit-Forchheimer formulation of a transport finite element model: application to remediation of a shallow, uncon fined aquifer

摘要

Groundwater contamination is frequently concentrated in the surficial or water-table aquifer. The first remediative step of aquifer clean-up consists of the extraction of the polluted water by pumping. Depending on the pumping rates, this may lead in situations where the surficial aquifer is shallow to significant drawdowns of the water-table. Modeling the horizontal solute transport in such a pumped unconfined aquifer by means of a classical 2D transport model that assumes a constant aquifer thickness, may lead to significant errors and, consequently, bias in the remediation strategy. Thus there is a desire to have an improved 2D solute transport model for simulating remediation in a phreatic shallow aquifer. In the present paper the well-known 2D SUTRA model is modified to include a Dupuit-Forchheimer formulation for unconfined aquifers which takes into account the laterally varying thickness of the water-bearing layer. The new model is validated by comparisons with analytical solutions and through testing of asymptotic consistency with the classical confined-aquifer solution. The model is used to simulate a possible remediation action in a shallow contaminated phreatic aquifer in Central Florida and to compute effective resident and clean-up times. These are compared with predictions obtained with the original SUTRA. The new Dupuit-SUTRA model predicts significantly shorter total clean-up times than the original model. The latter therefore gives a more conservative estimate of the remediation time. Budget calculations for the two model-versions reveal large differences in the total amount of contaminants extracted from the aquifer during the pumping process.