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Resolution of MRS Applied to the Characterization of Hard‐Rock Aquifers
Author(s) -
Legchenko Anatoly,
Descloitres Marc,
Bost Adelphe,
Ruiz Laurent,
Reddy Mohan,
Girard JeanFrançois,
Sekhar Muddu,
Mohan Kumar M.S.,
Braun JeanJacques
Publication year - 2006
Publication title -
groundwater
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.84
H-Index - 94
eISSN - 1745-6584
pISSN - 0017-467X
DOI - 10.1111/j.1745-6584.2006.00198.x
Subject(s) - aquifer , geology , borehole , depth sounding , porosity , groundwater , soil science , petrology , geotechnical engineering , oceanography
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 NUMIS plus 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.