Abstract
The protective capacity of aquifers is a prerequisite for groundwater quality in areas prone to contamination from the ground surface. Aquifers without protective layers are more susceptible to contaminations from point and non-point sources. The protective capacity of an aquifer significantly correlates with the thickness of clay and organic materials that mantled it. To assess aquifer protective capacity, electrical conductivity property of saturated clay was determined from filtered imaginary and real components of Very Low-Frequency Electromagnetic (VLF-EM). The filtered real components against distance and current density pseudo-section produced from real components were concomitantly used for interpretation. Clays capping aquifers were delineated from those without capping from low and high values of filtered imaginary and real components and current density pseudo-section. The distribution of clay laterally across the area indicates that aquifers are poorly protected and susceptible to contaminations from a point and non-point sources. The apparent agreement between inferred geology from VLF-EM interpretation, borehole data and resistivity data underscores the efficacy of VLF-EM as an important tool that can be used or combined with other geophysical methods and borehole information/data for assessment of the protective capacity of the aquifer.
Highlights
Aquifer vulnerability is a concept that describes the susceptibility of groundwater quality to contaminant loading [1] and is influenced by the inherent properties of the aquifer
The inadequacy commonly associated with the geophysical exploration of subsurface geology depends on the resolution and multiple possible interpretations; additional depends on the resolution and multiple possible interpretations; additional information information is often required for comparing acquired data with observed ones
The anomalous zones inferred from the quantitative interpretation of current density pseudo-sections and the plotted filtered real and imaginary components are the response of primary magnetic fields to conductors caused by clay materials in the subsurface
Summary
Aquifer vulnerability is a concept that describes the susceptibility of groundwater quality to contaminant loading [1] and is influenced by the inherent properties of the aquifer. Groundwater covering layers are necessary for the protection of an aquifer against imposed contaminant loading. The degree of protection is determined by the geologic material covering the aquifer. The type of geologic material covering aquifer is important as its presence or absence may act as a barrier or facilitate the infiltration of contaminants. It degrades contaminants through chemical, mechanical and biological processes. The availability of a barrier or its absence renders aquifers more or less vulnerable to migrating contaminants due to a low infiltration rate
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