A geoelectrical-hydrogeochemical investigation of shallow groundwater occurrence in Ibadan, southwestern Nigeria

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• 作者：A. I. Olayinka ; A. F. Abimbola ; R. A. Isibor and A. R. Rafiu
• 关键词：Key words  ; Crystalline basement complex ; Resistivity soundings ; Fracture trends ; Hydrogeochemistry ; Ibadan ; Southwestern Nigeria
• 刊名：Environmental Geology
• 出版年：1999
• 出版时间：January 1999
• 年：1999
• 卷：37
• 期：1-2
• 页码：31-39
• 全文大小：211 KB
• 刊物类别：Earth and Environmental Science
• 刊物主题：Earth sciences
  Geology
  
• 出版者：Springer Berlin / Heidelberg
• ISSN：1432-0495

文摘

 An integrated geological, geoelectrical and hydrochemical investigation of shallow groundwater occurrence in the Ibadan area, southwestern Nigeria, is presented. The primary objective was to characterise the groundwater in a typical low-latitude environment underlain by Precambrian crystalline basement complex rocks. The dominant rocks comprise suites of gneisses and quartzites. Chemical analyses of the groundwater show that the mean concentration of the cations is in the order Na>Ca>Mg>K while that for the anions is Cl>HCO<sub>3sub>>NO<sub>3sub>>SO<sub>4sub>. Statistical analyses, using the product-moment coefficient of correlation, indicate positive correlations between the following pairs of parameters: TDS and conductivity (r=0.96); Na++Mg2+ and Cl– (r=0.95); Na++K+ and Ca2+ (r=0.43); Na++K+ and HCO<sub>3sub> – (r=0.17); Ca2+ and Mg2+ (r=0.74); Ca2+ and HCO<sub>3sub> – (r=0.33); Ca2++Mg2+ and HCO<sub>3sub> – (r=0.31) and pH and HCO<sub>3sub> – (r=0.54). A very weak negative correlation was recorded between pH and Cl–, with r=–0.003. Five groundwater groups have been identified, namely, (1) the Na-Cl, Na-Ca-Cl, Na-Ca-(Mg)-Cl; (2) the Ca-(Mg)-Na-HCO<sub>3sub>-Cl, Na-Ca-HCO<sub>3sub>-Cl, and Ca-HCO<sub>3sub>-Cl; (3) the Ca-(Mg)-Na-HCO<sub>3sub>, Ca-Na-HCO<sub>3;sub> (4) Ca-Na-Cl-(SO<sub>4sub>)-HCO<sub>3sub> and (5) the Ca-(Mg)-Na-SO<sub>4sub>-HCO<sub>3sub>. The different groups reflect the diversity of bedrock types and consequently also of the products of weathering. Most of the water sampled is unfit for drinking on account of the high NO<sub>3sub> – content. It can, however, be used for irrigation purposes as the sodium hazard is low while the salinity hazard ranges from low to medium. Resistivity soundings indicate the presence of a thick weathering profile, which could be up to 60 m. Such sites should be the target for any long-term and sustainable groundwater development in the area.