Patrick Brunet 1* , Daniel Paradis 1&2 , René Lefebvre 1 , Erwan Gloaguen 1
1 Institut national de la recherche scientifique, Centre Eau Terre Environnement (INRS-ETE), 490 rue de la Couronne, Quebec City, QC, Canada G1K 9A9
2 Geological Survey of Canada, 490 rue de la Couronne, Quebec City, QC, Canada G1K 9A9
* Corresponding author: Patrick.Brunet@ete.inrs.ca
ABSTRACT (393 words)
Representative numerical models of flow and contaminant transport are needed to implement adequate and effective remediation actions at contaminated sites. Meaningful flow and transport modeling however depends on our capability to represent aquifer heterogeneities at the proper scale for the problem at hand.
To evaluate the ability of numerical models to reproduce the actual aquifer dynamics, which is in part controlled by aquifer heterogeneities, it is essential to have appropriate monitoring data (e.g., heads, concentrations, flux) that reflect representative hydrogeological conditions. Vertical profiles of hydraulic head are controlled by the distribution and continuity of the hydrofacies (HF) and their corresponding hydraulic conductivity (K). Such profiles can thus be used to constrain determinist or stochastic representations of heterogeneity in numerical models.
To assess the potential of vertical hydraulic head profiles to define aquifer heterogeneity at a sub-watershed scale, a characterization program was carried out in a highly heterogeneous and anisotropic littoral aquifer system located in Saint-Lambert-de-Lauzon,
Quebec.
A total of 24 CPT/SMR soundings were first carried out and transposed into soil texture classes to select intervals for hydraulic head monitoring.
Nineteen (19) intervals in 9 fully-screened wells were instrumented to get continuous profiles of hydraulic head over a period of 1 year and detailed (every 30 cm) static hydraulic head profiles were also acquired in 8 of these wells. Head profiles were acquired from a series of pressure transducers isolated between packers . To investigate the impact of HF distribution and continuity on vertical head profiles, different scenarios of heterogeneity were generated on a 2D vertical section along a groundwater flow line.
The various scenarios of heterogeneity were simulated from HF data generated from available CPT/SMR soundings located along the 2D section using the Multiple Point
Geostatistics (MPG) algorithm IMPALA.
Statistical relations defined in a previous study for a representative subset of CPT/SMR and hydraulic conductivity measurements allowed subsequent prediction of HF memberships and K from CPT/SMR data alone. Vertical head profiles were then extracted from the flow simulations carried out on typical continuous and discontinuous geostatistical realizations.
To assess the capacity to reproduce the original heterogeneous distribution of HF from the extracted head profiles, inverse simulations using the gradual deformation method (GDM) were used. Simulation results show that the potential of head profiles to constrain aquifer heterogeneity depends mainly on the distance between profile locations, the HF lateral continuity and K contrasts between HF.
Key words: heterogeneity, hydraulic conductivity, hydraulic head, CPT, hydrostratigraphic model, geostatistics, numerical modeling