Delineation of groundwater provenance in a coastal aquifer using statistical and isotopic methods,Southeast Tanzania   总被引：4，自引：3，他引：1  

Said Suleiman Bakari  Per Aagaard  Rolf D. Vogt  Fridtjov Ruden  Ingar Johansen  Said Ali Vuai 《Environmental Earth Sciences》2012,66(3):889-902

Rapid population growth and urbanization has placed a high demand on freshwater resources in southeast costal Tanzania. In this paper, we identify the various sources of groundwater and the major factors affecting the groundwater quality by means of multivariate statistical analyses, using chemical tracers and stable isotope signatures. The results from hierarchical cluster analyses show that the groundwater in the study area may be classified into four groups. A factor analysis indicates that groundwater composition is mainly affected by three processes, accounting for 80.6% of the total data variance: seawater intrusion, dilution of groundwater by recharge, and sewage infiltration. The hydrochemical facies of shallow groundwater was mostly of the Na–Ca–Cl type, although other water types were also observed. The deep groundwater samples were slightly to moderately mineralized and they were of the NaHCO₃ type. This water type is induced mainly by dissolution of carbonate minerals and modified by ion exchange reactions. The signal from the stable isotope composition of the groundwater samples corresponded well with the major chemical characteristics. In the shallow groundwater, both high-nitrate and high-chloride concentrations were associated with localized stable isotope enrichments which offset the meteoric isotopic signature. This is inferred to be due to the contamination by influx of sewage, as well as intrusion by seawater. The depleted stable isotope values, which coincides with a chemical signature for the deep aquifer indicates that this deep groundwater is derived from infiltration in the recharge zone followed by slow lateral percolation. This study shows that a conceptual hydrogeochemical interpretation of the results from multivariate statistical analysis (using HCA and FA) on water chemistry, including isotopic data, provides a powerful tool for classifying the sources of groundwater and identifying the significant factors governing the groundwater quality. The derived knowledge generated by this study constitutes a conceptual framework for investigating groundwater characteristics. This is a prerequisite for developing a sound management plan, which is a requirement for ensuring a sustainable exploitation of the deep aquifer water resource in the coastal area of Tanzania.  相似文献   

Deep low-salinity groundwater in sedimentary basins: petrophysical methods from a case study in Somalia     

Quiroga  Elizabeth  Bertoni  Claudia  Ruden  Fridtjov 《Hydrogeology Journal》2023,31(3):685-705

Oil and gas exploration data for the Northern Somalia and Horn of Africa region have been utilised for deep freshwater resources exploration. This unique geophysical and petrophysical dataset is integrated into a regional hydrogeological study and it allows for targeting of unmapped and unknown deep aquifers that would otherwise be beyond the conventional reach of the groundwater sector. The database includes open-hole well logging surveys (resistivity, gamma ray, and spontaneous potential), mud logging and drill stem test (DST) data. The results from the data analysis are combined with the geological interpretation to assess the freshwater potential of each mapped hydrostratigraphic unit in the region. The results highlight the presence of several previously unknown deep low-to-medium salinity (<9  g/L total dissolved solids (TDS)) aquifers within the Jurassic to Eocene units, including the Adigrat, Hamanlei, Gabredarre, Gumburo, Jessoma, and Auradu formations. With tested intervals of water containing less than 3.8 g/L total dissolved solids, the Auradu, Jessoma, and Gumburo formations are the most promising deep freshwater aquifers. Additional results on the analysis of groundwater parameters, such as hydraulic head, provide the basis for further groundwater modelling. The results show that the method has good potential, in particular for use in drought-stricken areas of arid regions. Ultimately, the results from this region have global significance, as the method can provide a new means of boosting fresh groundwater resources in water-poor regions, and supporting sustainable development and utilization of the resources in the medium and long term.

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