Browsing by Author "Ayodeji, Olufemi Samson"

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    Preliminary characterization of groundwater resources in Arusha region, Tanzania
    (University of Dar es Salaam, 1992) Ayodeji, Olufemi Samson
    The study attempted a preliminary characterization of Arusha region with distinctive groundwater characteristics through interpretation of maps, satellite imagery and historical data of boreholes drilled in the region. Three hydrogeologic zones in the region -Volcanic, Basement complex and unconsolidated sedimentary zones have been demarcated. The hydrogeologic features consist of mostly an internal drainage basin and to a lesser extent partly Indian Ocean drainage basin on the north eastern part and Mediterranean drainage basin on the north western part. Groundwater occurs mainly at depths of 40 m.b.g.l and rarely down to 160 m.b.g.l in fractured zones, weathered surfaces in basement complex rocks, unconsolidated sedimentary deposits and volcanic rocks. The mean yield of wells drilled in sedimentary deposits was 141 m3/day. However, the mean yield of wells drilled in basement rocks and volcanic rocks was 142.8 m3/day and 304 m3/day respectively. Most of the springs in volcanic areas in Arusha town are perennial yielding total discharges up to 20,000 m3/day during the raining season and a minimum of 10,000 m3/day during the dry season. Other springs from different parts of the region have not yet been adequately utilized. Different well design options were considered for each of the hydrogeologic zones. Three well design options were recommended for shallow wells based on the rock types. Similarly, different types of well screens and casings for deep boreholes were considered. The chemistry of 191 water samples from boreholes and springs from different parts of Arusha region were analyzed. 15% of the water samples from boreholes and about 45% of the spring water had high fluoride concentration above 1.5 parts per million that is above the WHO permissible limit for drinking water; while about 2% and 50% respectively are above 8 ppm, the Tanzanian permissible limit for drinking water. High fluoride content tends to coincide more with volcanic rock than in the other hydrogeologic units. Groundwater zones having excessive fluoride concentration will require defluoridation. However, some places contain high total dissolved solids (TDS).