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Resolution of MRS Applied to the Characterization of Hard-Rock Aquifers

Abstract : The performance of the Magnetic Resonance Sounding (MRS) method applied to the investigation of heterogeneous hard-rock aquifers was studied. It was shown using both numerical modeling and field measurements that MRS could be applied to the investigation of the weathered part of hard-rock aquifers when the product of the free water content multiplied by the thickness of the aquifer is >0.2 (for example, 10-m-thick layer with a 2% water content). Using a currently available one-dimensional MRS system, the method allows the characterization of two-dimensional subsurface structures with acceptable accuracy when the size of the subsurface anomaly is equal to or greater than the MRS loop. However, the fractured part of hard-rock aquifers characterized by low effective porosity (<0.5%) cannot be resolved using currently available MRS equipment. It was found that shallow water in the weathered part of the aquifer may screen MRS signals from deeper water-saturated layers, thus further reducing the possibility of investigating deeper fractured aquifers. A field study using the NUMISplus MRS system developed by IRIS Instruments was carried out on an experimental watershed in southern India. A heterogeneous unconfined aquifer in a gneissic formation was successfully localized, and MRS results were confirmed by drilling shortly after the geophysical study. The top of the aquifer revealed by MRS was found to be in a good agreement with observed static water level measurements in boreholes.
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Submitted on : Wednesday, May 20, 2009 - 11:25:02 AM
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Anatoly Legchenko, Marc Descloitres, Adelphe Bost, Laurent Ruiz, Mohan Reddy, et al.. Resolution of MRS Applied to the Characterization of Hard-Rock Aquifers. Groundwater, Wiley, 2006, 44 (4), pp.547 à 554. ⟨10.1111/j.1745-6584.2006.00198.x⟩. ⟨insu-00385829⟩



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