Enhancement of remediation pilot test data using groundwater modelling: a case study

In groundwater remediation, Groundwater Circulation Wells (GCW) are used as an alternative to typical Pump & Treat (P&T) methods. Extraction and injection are operated in a single well with multiple isolated screened intervals, which creates a three-dimensional flow pattern (circulation cell) in the aquifer. The utility of GCW pump test data can be increased using groundwater modelling to assess remediation feasibility. Simulating pilot tests gives a unique opportunity to calibrate key flow parameters such as vertical hydraulic conductivity (Kv) and better definition of hydrogeologic units. GCW pump tests were simulated using both steady-state and transient MODFLOW models. This paper describes modeling hypotheses, grid design, boundary conditions and material properties. The calibration procedure is then discussed in detail including sensitivity studies and automatic calibration. Finally, advantages and drawbacks are listed as well as likely improvements including the use of a finite-element code to more accurately simulate radial flow. Using both trial-and-error and automated techniques enabled focused and efficient model calibration. This study was a pioneering work and contributed in installing the first GCWs in Belgium. It provided a stronger basis to demonstrate the effectiveness of GCW technologies and played a key role in the acceptance of the remedial plan by local regulators.