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Tanta University (2019)

Groundwater Quality Assessment Integrating Hydrochemical and Geophysical Techniques in El-Hammam District, Northwestern Coast, Egypt

El-Berry, Eman Hamed Mohamed.

Titre : Groundwater Quality Assessment Integrating Hydrochemical and Geophysical Techniques in El-Hammam District, Northwestern Coast, Egypt

Auteur : El-Berry, Eman Hamed Mohamed.

Etablissement de soutenance : Tanta University

Grade : Master of Science (MSc) in Geology 2019

Résumé partiel
Groundwater is a vital resource for drinking and irrigation especially in arid and semiarid provinces. Groundwater quality degradation is an issue of significant societal and environmental concern. The quality of water as a world resource is diminishing rapidly due to the substantial increases in industrialization, urbanization and the expansion of agricultural activities. The main purpose of the present study is to assess the groundwater quality integrating the hydrochemical data obtained from forty-two wells, the geoelectric resistivity measurements of 16 Schlumberger Vertical Electrical Sounding (VES), and 8 seismic profiles to elucidate the subsurface lithological variations. This is to find a key relationship between the hydrochemical properties of the groundwater affecting its quality along with the resistivity and the seismic response of the aquifer. The approach is applied to deduce the first insights of the integrated techniques in El Hammam area, located on the NW Coast of Egypt. Three subsurface layers were detected from the interpreted resistivity results of the measured sounding points, seismic profiles and their close sampled wells ; topsoil alluvium calcareous loam layer, water-bearing oolitic limestone, and clay deposits. The alluvial layer has seismic velocity range of 0.4 - 0.7 km/sec, 1 – 20 Ω.m resistivity values, and 0.5 - 8 m thickness. This decrease in the resistivity from the surface downwards is attributed the increase in moisture content. The limestone showed velocity range of 2 - 2.7 km/sec, 6 - 60 Ω.m resistivity, and 3-45 m thickness. The limestone contains thin evaporite lenses mostly gypsum with resistivity range from (90-300 Ω.m), (5-10 m thick) with 0.8-1.6 km/sec velocity range as indicated by the shallow seismic refraction method. The third layer is made up of clay with top surface range of 4.5 - 59 m and extends downward. Lower resistivity values in the oolitic aquifer associated with large Total Dissolved Solids (TDS) attributed mostly to the dissolution of the evaporite lenses and/or to seawater intrusion. Nitrates showed local highs mostly from the application of excessive fertilizers in agricultural areas. Many geoelectric cross-sections were constructed to reveal the lateral and vertical hydro-lithological variations in the study area such as A-A’, B-B’, CC’, D-D’ and E-E’ as they contain complete view of the data. Cross-sections A-A’, B-B’, C-C’ are oriented NE–SW parallel to the coast. Cross-sections DD’ and E-E’ are oriented N–S perpendicular to the coast. Profile A-A’ includes soundings stations 11, 12, 13, 14, 15, and 16. Interpreted resistivity values of water-bearing formations observed from these soundings are from 6 to 60 Ω.m. In general, aquifer layer considered limited thickness and slightly brackish layer. Only in VES11, 14, and 15 the fresh water which has true resistivity ranging from 50 to 60 Ω.m affected by the seepage of Bahig canal. This recharge confirmed by TDS of well no.7 (883mg/l) which nearest to sounding no.11. Profile B-B’ includes soundings stations 10, 9, 8, 7 and 6. Interpreted resistivity values of oolitic limestone aquifer ranged from10 and 40 Ω.m. This brackish layer (10–40 Ω.m) is thicker towards NE and VES 8, 9 and 10. The thickness of this layer varies from 3 m at sounding no 7 to 48 m at sounding no 9. Groundwater drawn from wells 29, 40, 19 which adjacent to soundings no.6, 7 and 8 respectively was found to be brackish (TDS >1000 mg/l) and it originates from brackish zone with resistivities alternative from 10-30 Ω.m. TDS of former wells is 1590, 1475 and1820 mg/l respectively. The second geoelectric layer of oolitic limestone aquifer included evaporite lenses mostly gypsum extended between soundings no.8 and no.9 under surface layer.

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Page publiée le 28 décembre 2020