Investigation of groundwater occurrences and potential sources for groundwater pollution by joint application of geophysical and hydrochemical approaches: a case study of some urban cities at West Ismailia, Egypt

This study chose the area west of Ismailia city due to its relevant socio-economic importance and the hydrogeological challenges it faces. This area's primary water source is the groundwater due to a lack of clean surface water resources. So, this study aims to characterize the principal groundwater aquifers in the investigated area by applying integrated geophysical techniques, including Vertical Electrical Sounding (VES) and Time Domain Electromagnetic (TEM). In addition, we Study the reasons for the water logging problem that threatens all the agricultural activities in the study area by applying Electrical Resistivity Tomography (ERT) near some lakes resulting from this waterlogging. Our final aim is to investigate the possible sources of contamination and deterioration in water quality by hydrochemical analysis. In this concern, 35 VES and TEM data point stations were applied along five parallel profiles trending N-S through the study area. The VES and TEM data points were acquired nearly at the same sites to be suitable for joint inversion. VES data were collected by SYSCAL R2 instrument using Schlumberger array while the TEM data were collected by SIROTEM MK3 using the standard square single loop with 100 m length side. Then VES data was inverted by IPI2WIN 1-D while TEMIX XL4 inverted the TEM data. The Curupira program performed the joint inversion between both two methods. In order to achieve our second purpose regarding the water logging problem, 11 ERT profiles were conducted through the study area, where 11 profiles were applied around one of the biggest lakes that resulted from this problem. In contrast, the last profile was applied far away from these lakes to compare the behaviour of ERT in both of them. The data was collected by the SYSCAL R2 instrument and then inverted using the RES2DINV program. Hydrochemical analyses were applied to 15 water samples collected from some of the available water wells in the study area to study groundwater quality. These samples were collected along two profiles directing N-S. The analyses were made in the "Central Laboratories of the National Water Research Centre (NWRC)". From the VES and TEM data processing and interpretation, two aquifer systems were identified in the area, Pleistocene and Miocene aquifers; where the Pleistocene aquifer is the principal aquifer in the study area consisting of successive layers of gravel and sand and sand with many clay lenses of fluviatile origin. The upper surface of the Pleistocene aquifer could be detected at depths from 10 to 83 m below the ground surface, with a total thickness ranging from 129 m to 273 m. Its resistivity ranges between 4 to 95 Ωm. It is lying uncomfortably on the Miocene aquifer. Due to the subsurface structural complexity, a possible lateral seepage of saline water can occur from the Miocene aquifer into the Pleistocene one. The Miocene aquifer lies at depths ranging from 130 to 328 m below the ground surface. It is mainly composed of marine marly sandstone and limestone, showing relatively low resistivity values ranging from 6 to 22 Ωm. The groundwater within this aquifer is mainly saline. From ERT data inversion and interpretation, three geoelectrical units were revealed. The middle unit, mainly composed of evaporitic loamy sand, is responsible for the water logging problem that threatens the study area. The detailed hydrochemical analysis revealed that trace and heavy metals are present in deficient concentrations in all samples collected from the study area and have no effect on groundwater quality. About 75% of the collected samples are characterized by high TDS (>3000), thus exceeding the allowed limits approved by WHO and local authorities, except for the samples collected from Wadi El-Tumilat. As a result of this high salinity, this water is not suitable for drinking or domestic use.