Evaluation of exploration and monitoring methods for verification of natural attenuation using the virtual aquifer approach

Though natural attenuation (NA) is increasingly considered as a remediation technology, the methods for proper identification and quantification of NA are still under discussion. Here the "Virtual Aquifer" approach is used to demonstrate problems which may arise during measurement of concentrations in observation wells and for interpolation of locally measured concentrations in contaminated heterogeneous aquifers. The misinterpretation of measured concentrations complicates the identification and quantification of natural attenuation processes. The "Virtual Aquifer" approach accepts the plume simulated with a numerical model for a heterogeneous aquifer as "virtual reality". This virtual plume is investigated in the model with conventional methods like observations wells. The results of the investigation can be compared to the virtual "reality", evaluating the monitoring method. Locally determined concentrations are interpolated using various interpolation methods and different monitoring set-ups. The interpolation results are compared to the simulated plume to evaluate the quality of interpolation. This evaluation is not possible in nature, since concentrations in a heterogeneous aquifer are never known in detail.