Integrated TEM and 2DERI techniques to delineate groundwater bearing zones in fractured carbonate rocks at the upstream portion of wadi Halazeen, Northwestern Coast, Egypt

Abstract

The increasing reliance on groundwater as supplementary water resource for the decreasing rainfall in the Northwestern Coastal Zone of Egypt (NWC) makes groundwater exploration and aquifers characterization in that area of particular importance. A representative locality for the conditions under which groundwater occurs in NWC is the upstream portion of Wadi Halazeen, which lies some 37 km to the west of Mersa Matruh city. In the present work, integrated Transient electromagnetic (1DTEM) and two-dimensional electrical resistivity imaging (2DERI) has been conducted to explore and characterize the groundwater of Miocene aquifer in the upstream portion of Wadi Halazeen. A total of 25 TEM soundings along with 5 normal and reciprocal profiles of 2DERI were measured. The lithological data of the borehole has been used to parameterize the inversion of the geophysical data. In order to maximize the reliability of the inversion results, the acquired data is subjected to some processing such as smoothing, editing and removing depending on TEM sounding significance plus computing reciprocal error of 2DERI measurements. The inversion results of both geophysical methods indicated that the geoelectrical succession consists of five layers along with the surface weathered layer (Dolomitic limestone, Sandy limestone, limestone, marly limestone and clay). The results indicated also that facies change is a common feature characterizes most of the layers. This feature controls groundwater occurrence within the fifth layer where the lithological composition of this layer changes from fractured limestone to marly limestone to marl and clay. Groundwater exists in a channel-like zone of fractured limestone and marly limestone which extends from south to north in the study area. Generally, the groundwater salinity of the study area and neighboring groundwater wells tapping the fractured Miocene aquifer are range between 2900 and 4268 ppm, while the groundwater of DRC5 well which lays in the watershed area has a relatively lower salinity value (1482 ppm) where it receives large recharge related to annual precipitations and surface runoff water than area of outside basin boundary divides. Integration of the results of 1DTEM and 2DERI delivered plausible information about the groundwater occurrence in fractured carbonate rocks.