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Article

3D Characterization of a Coastal Freshwater Aquifer in SE Malta (Mediterranean Sea) by Time-Domain Electromagnetics

1
Department of Geology and Geophysics, Texas A&M University, College Station, TX 77843, USA
2
Marine Geology and Seafloor Surveying, Department of Geosciences, University of Malta, MSD 2080 Msida, Malta
3
GEOMAR—Helmholtz Centre for Ocean Research Kiel, Wischhofstraße 1-3, D-24148 Kiel, Germany
*
Author to whom correspondence should be addressed.
Water 2020, 12(6), 1566; https://doi.org/10.3390/w12061566
Received: 27 March 2020 / Revised: 21 May 2020 / Accepted: 27 May 2020 / Published: 30 May 2020
(This article belongs to the Special Issue Applied Geophysics in Hydrogeological Practice)
Electromagnetic (EM) geophysical methods are well equipped to distinguish electrical resistivity contrasts between freshwater-saturated and seawater-saturated formations. Beneath the semi-arid, rapidly urbanizing island of Malta, offshore groundwater is an important potential resource but it is not known whether the regional mean sea-level aquifer (MSLA) extends offshore. To address this uncertainty, land-based alongshore and across-shore time-domain electromagnetic (TDEM) responses were acquired with the G-TEM instrument (Geonics Ltd., Mississauga, ON, Canada) and used to map the onshore structure of the aquifer. 1-D inversion results suggest that the onshore freshwater aquifer resides at 4–24 m depth, underlain by seawater-saturated formations. The freshwater aquifer thickens with distance from the coastline. We present 2D and 3D electromagnetic forward modeling based on finite-element (FE) analysis to further constrain the subsurface geometry of the onshore freshwater body. We interpret the high resistivity zones that as brackish water-saturated bodies are associated with the mean sea-level aquifer. Generally, time-domain electromagnetic (TDEM) results provide valuable onshore hydrogeological information, which can be augmented with marine and coastal transition-zone measurements to assess potential hydraulic continuity of terrestrial aquifers extending offshore. View Full-Text
Keywords: coastal hydro-geophysics; groundwater; mean sea-level aquifer; transient electromagnetics coastal hydro-geophysics; groundwater; mean sea-level aquifer; transient electromagnetics
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MDPI and ACS Style

Pondthai, P.; Everett, M.E.; Micallef, A.; Weymer, B.A.; Faghih, Z.; Haroon, A.; Jegen, M. 3D Characterization of a Coastal Freshwater Aquifer in SE Malta (Mediterranean Sea) by Time-Domain Electromagnetics. Water 2020, 12, 1566. https://doi.org/10.3390/w12061566

AMA Style

Pondthai P, Everett ME, Micallef A, Weymer BA, Faghih Z, Haroon A, Jegen M. 3D Characterization of a Coastal Freshwater Aquifer in SE Malta (Mediterranean Sea) by Time-Domain Electromagnetics. Water. 2020; 12(6):1566. https://doi.org/10.3390/w12061566

Chicago/Turabian Style

Pondthai, Potpreecha, Mark E. Everett, Aaron Micallef, Bradley A. Weymer, Zahra Faghih, Amir Haroon, and Marion Jegen. 2020. "3D Characterization of a Coastal Freshwater Aquifer in SE Malta (Mediterranean Sea) by Time-Domain Electromagnetics" Water 12, no. 6: 1566. https://doi.org/10.3390/w12061566

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