Using vertical head profiles to constrain the geostatistical representation of heterogeneity in a shallow granular aquifer

Patrick Brunet, Daniel Paradis, René Lefebvre, Erwan Gloaguen

Dans les comptes rendus d’articles de la conférence: GeoMontréal 2013: 66th Canadian Geotechnical Conference; 11th joint with IAH-CNC

Session: General Hydrogeology I

ABSTRACT: 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 hydrofacies (HF; materials with distinct hydraulic properties) 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, we developed an approach combining the use of cone penetration tests (CPT) and soil moisture-resistivity (SMR) measurements with detailed vertical hydraulic head profiles in fully-screened observation wells. 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 (figure 1). Figure 1. Field setup of head profile measurement (left). Study site head profile (well P5) and corresponding Eslami-Fellenius facies interpretation from CPT/SMR data (right).

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