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العنوان
Groundwater Quality Assessment Integrating Hydrochemical and Geophysical Techniques in El-Hammam District, Northwestern Coast, Egypt /
المؤلف
El-Berry, Eman Hamed Mohamed.
هيئة الاعداد
باحث / ايمان حامد محمد البرى
مشرف / علاء احمد مسعود
مشرف / عبدالعزيز خيرى عبد العال
مشرف / لايوجد
الموضوع
Geology.
تاريخ النشر
2019.
عدد الصفحات
179 p. :
اللغة
الإنجليزية
الدرجة
ماجستير
التخصص
الجيولوجيا
تاريخ الإجازة
16/10/2019
مكان الإجازة
جامعة طنطا - كلية العلوم * - الجيولوجيا
الفهرس
Only 14 pages are availabe for public view

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Abstract

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. Lower resistivity values in the oolitic aquifer associated with large Total Dissolved Solids (TDS) attributed mostly the dissolution of the evaporite lenses. Lower resistivity values also in the third layer which composed clays and sandy clay is also due to seawater intrusion. Profile C–C’ includes soundings stations no.1, 2, 3 and 4. Profile C–C- is same with profile B–B- except the thickness of surface layer (alluvium calcareous loam) is relatively larger in profile C–C’ than profile B –B’, the low resistivity values of oolitic limestone aquifer ranged 10-20 Ω.m is due to profile C–C- located in the north of study area towards Mediterranean sea and evaporite lenses of gypsum are located between soundings on.2 and no.3. Profile D-D’ includes soundings stations 5, 4, 10 and 11. Interpreted resistivity values of oolitic limestone aquifer ranged from 20-200 Ω.m. The brackish layer (20 Ω.m) is thicker towards VES 4 and 10. The second geoelectric layer of oolitic limestone aquifer included evaporite lenses mostly gypsum at VES no.10 under surface layer. Lower resistivity values in the oolitic aquifer associated with large Total Dissolved Solids (TDS) attributed mostly to the dissolution of the evaporite lense. Profile E-E’ includes VES stations, (1, 6 and 15). This section indicates the same layers arrangement and the same decreases in apparent resistivity from S-N as the former sections. we can summarize the results of electrical resistivity investigation in the following points: 1. Variation of resistivity values and the soil permeability values of the alluvium layer in the Piedmont Plain reflecting heterogeneities of this layer which becomes threat source for oolitic limestone aquifer layer by pollution and direct effect in the depth to water. 2. Variation of resistivity values of oolitic limestone aquifer layer reflect variations of the groundwater quality from slightly freshwater in south to brackish water in north where the northern parts approaching the Mediterranean Sea. 3. Thickness of aquifer layer increases from south to north and northeast. 4. High relatively of resistivity values (50-60 ohm ) in the south of the study area around sounding 11,14 and 15 reflect seepage of Bahig canal to the aquifer layer. 5. Low resistivity values in different places of aquifer layer reflect high salinity which attributed to presence of lenses of evaporite. The hydrochemical analysis showed that the salinity of groundwater ranges from a relatively fresh water zone (TDS < 1000 mg/l) near to (Bahig canal) to a slightly saline (TDS 1000–3000 mg/l) in most water samples. Towards Mallahet Mariut and Mediterranean Sea, the groundwater is moderately saline (3000 and 10,000 mg/l TDS) with TDS >3000(samples no.8, 12, 13and 33). But the high relatively of salinity (4380 and 4100 mg/l) of samples nos.20 and 21 located close to the Bahig canal due to dissolution of the evaporite lenses. Quality assessment according to WHO (2011), Ministry of Health (2007) and USEPA(2009) standards for drinking water clarified that most of the water samples is unsuitable for domestic uses on account of high TDS and nitrate contents. Irrigation classification for water samples clarifies that groundwater in Pleistocene oolitic limestone may not be suitable for irrigation on soils with poor drainage without management for salinity control. The general direction of groundwater flow is from the south to the north. The depth to water is actually decreasing in comparison with the previous studies. This is due to the canal water seepage and irrigation return flow in these new reclaimed lands. Depending on Gilbert table (Gilbert, 1999), the interpretation of seismic refraction results clarifies the same layers shown in the electrical results. Based on the results of this study, it is recommend that: 1. Modern irrigation systems should be introduced to the farmers, which in future may result in a more sustainable use of the existing groundwater resources. 2. Management and protection of groundwater resources should be controlled by responsible government agencies in addition to the participation of the local community on the basis of a water policy designed to determine the safe yield. 3. Electrical resistivity measurements should be carried out prior any drilling operations for delineating the most appropriated sites in regarding to their salinity and thickness of the aquifers. 4. Applying fertilizers in the proper amount in agricultural practice as fertilizers contains chemicals that cause water pollution. 5. A periodic water quality assessment is necessary to evaluate any deterioration of water quality in the area.