Deterministic and stochastic modelling for protection zone delineation

Protection zones delimited by isochrones are often computed using calibrated groundwater flow and transport models. In heterogeneous formations, all direct (hard) and indirect (soft) data must be used optimally. Approaches involving in situ pumping and tracer tests, combined with geophysical and/or other geological observations, should be developed. In a deterministic framework, the calibrated model is considered to be the best representation of reality at the current investigation stage, but uncertainty of the results is not quantified. Using stochastic methods, a range of equally likely isochrones can be produced, allowing us to quantify the influence of our knowledge on the aquifer parameters on protection-zone uncertainty. Furthermore, integration of soft data in a conditioned stochastic generation process, possibly associated with an inverse modelling procedure, can reduce the resulting uncertainty. Proposed is a stochastic methodology for protection-zone delineation, integrating hydraulic conductivity measurements (hard data), head observations and electrical resistivity data (soft data).