Applying of SP, DC-Resistivity, DC-TDIP and TDEM soundings in high saline coastal aquifer

Abstract

Four surface geophysical techniques were utilized to study the geological and hydrogeological settings of highly saline a coastal aquifer system to the north-east of River Nile Delta, Egypt. These techniques include SP, DC-Resistivity, TDIP and TDEM methods. The first target was to determine the geological stratification as a differentiation among clay, clayey, sand and sandy layers of high saline water. These techniques reflect that there is a complicated lateral and vertical difference in sediments along study area. The surface layers with depth down to ~120 m have low to medium content of clay that change with depth. Then, the second target was the differentiation laterally and vertically for salinity with depth down to ~250m as an interesting hydrogeological setting. These techniques reported that the sediments consist of thin and thick clay and silts, clayey sand, and sandy clay strata. Investigation depth was up to ~210m due to high salinity and clay content effect. At shallow depths, soil texture (down to ~100m and sometimes down to ~160m) consists of clay and silt with sand intercalation. The TEM data indicate a zone of less saline water and low clay content starting from ~40 to ~100m. There may be an evidence for a significant high to medium clay content after these depths down to ~250m. All four methods were calibrated with each other. Accordingly, good matching between the inversion model of TEMSs and composite logs of new drilled well was found, especially in lithological layers identifications. Also, this calibration confirmed that the area was complicated regarding the geological and hydrogeological conditions and the TDIP and TEM are the best methods in studying the environmental, geological and hydrogeological settings as primary important engineering implications for studying coastal highly saline aquifers.