Document Details
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Document Type |
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Thesis |
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Document Title |
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Integration of Geophysical Methods for Investigating Contaminant Distribution at Wadi Uranah, Makkah Al-Mukarramah, Saudi Arabia تكامل الطرق الجيوفيزيائية لتقصي توزيع التلوث في وادي عرنة، مكة المكرمة، المملكة العربية السعودية |
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Subject |
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Faculty of Earth Sciences |
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Document Language |
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Arabic |
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Abstract |
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This study aims to incorporate the analysis and interpretation of aeromagnetic data and ground magnetic survey with the results of vertical electrical sounding and electric resistivity tomography to discriminate between sites that are impacted by triple treated sewage water and sites that are still dominated by the effect of the residual contaminant plume caused by earlier dump of untreated wastewater at the downstream of Wadi Uranah. It is also the aim of this study to investigate the subsurface geological and structural elements controlling the flow and accumulation of contamination.
The geological structures, inferred from the magnetic studies, reveal the existence of groups of normal faults. The general trends of the normal faults are: NW, NE, NNE, NNW, WNW, N-S, E-W, ENE, NWN, NNE, NWW, and NEE. The occurrence of these normal faults creates grabens that trend in the direction of NW and NE direction. These faults and grabens control the migration and accumulation of the contaminant plumes at the downstream of Wadi Uranah. This scenario justifies the SW spreading of pollution at this part of the study area. The effect of the sewage pollution is generally scarce in the northeast, north and southeast of the sewage water channel as indicated by the high resistivity values at these sites. This can be attributed to the fact that the sewage water channel is bounded by uplifted basement blocks due to the occurrence normal faults that are associated with Red Sea development. At the southwestern part of the study area, low resistivity values may be attributed to the presence of faults trending parallel to the Red Sea. This geological structure acts as a barrier to the progress the sewage contaminant plume.
The Vertical Electrical Sounding (VES) survey has resulted in a number of geoelectric models ranging between three, four, and five geoelectrical layers. The first two or three layers correspond to the unsaturated zone that consists of aeolian sediments comprising sand and silt carried by wind. The electrical resistivity of the unsaturated zone ranges between 62 and 2192 Ωm and its thickness ranges between 0.267 and 28 m. The saturated zone shows high, moderate and low electrical resistivity depending on the location. The high electric resistivity layer represents the percolation that has been occurred for the carrying groundwater layer by treated sewage water (39 Ωm). The moderate electric resistivity layer represents the layer that is impacted partially by the treated sewage water infiltration (13 Ωm). While, the low resistivity layer (1 Ωm -5 Ωm) indicates the absence of the impact of the triple treated sewage water at these locations. Therefore, the groundwater at these locations corresponds to the residual contaminant plume and no infiltration for the tribble-treated sewage water has been occurred. The depth of the layer impacted by the treated sewage water ranges between 1.5m and 32 m. The impact of the treated sewage water is confined to sits located at distance of less than 1 km away from the sewage water channel. In general, the southwest direction is the preferable trend for the subsurface flow and accumulation of the groundwater, and hence the contamination at the downstream of Wadi Uranah.
The hydrochemical analysis illustrates that the impact of dumping triple treated sewage water reduces significantly the values of the Total Dissolved Solids (TDS) concentration. Accordingly, the quality of the groundwater could be classified into three groups based to their TDS concentration. The first group is characterized by low values in TDS concentration with average value of 996 mg/l. The average value for the TDS concentration of the second group is 1611 mg/l, while the average value for the TDS concentration of the third group is 5266 mg/l. The infiltration or percolation of the triple treated sewage water through the shallow alluvium aquifer and washing the contamination plume is very clear at wells that belong to the first group, while the mixing the triple treated sewage water is partial or limited at wells belonging to the second group. The high value of the mean TDS concentration of the third group indicates that the impact of the triple treated sewage water is totally absent. Therefore, the groundwater at these location corresponds to the residual contaminant plume and no infiltration for the Tribble treated sewage water has been occurred.
In conclusion, the integrated results show that the contamination flow and accumulation are controlled mainly by the subsurface faults and basement topography. Subsurface faults form pathways for the contamination, while subsided basement blocks form basins with thick sedimentary cover, suitable for accumulation of the contamination. The results also show that years of dumping untreated sewage water has created a significant contamination in the area. The current dump of tribble treated sewage water gradually dilutes or washes away this contamination in the vicinity of the sewage water channel. This dilution effect, however, is limited to an area of about 1 km around the sewage water channel. |
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Supervisor |
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Prof. Dr. Mohamed Ahmed Rashed |
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Thesis Type |
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Doctorate Thesis |
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Publishing Year |
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1440 AH
2018 AD |
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Added Date |
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Monday, December 10, 2018 |
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Researchers
| نورالدين مجتبى الاندنوسي | Al-Andoonisi, Nooruddin Mojtaba | Researcher | Doctorate | |
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