Values of δD and δ¹⁸O and concentrations of ³H and ¹⁴C of deep groundwater in Djibouti

抄録

In Djibouti, as the amount of the fresh water is not large enough, deeper groundwater recharged in the volcanic aquifer has been developed and it is considered to be a new source of fresh water in most of the region of the country. Although some studies have been conducted to find out the volume, depth, quality and age of groundwater, the data is not still enough to construct a scheme of agricultural development using the deeper groundwater in large area of Djibouti. Therefore, the first purpose of this study is to estimate the original recharged area of the deeper groundwater of this country, using stable isotope (δD and δ¹⁸O) analysis, and secondary to calculate the age of groundwater, using radioactive isotope (³H and ¹⁴C) analysis. We have collected groundwater samples from 16 wells in 4 districts (Djibouti City, Arta, Ali-Sabieh, and Dikihil) in 2019. The results on δD and δ¹⁸O showed a possibility that the recharge areas were not simple in the complicated geological condition with lots of various faults even the location of wells is close. The concentration of ³H on the 6 samples was very low (under 0.3 T. U.), indicating that the age of the groundwater samples was older than 70 years.