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22 nd Salt Water Intrusion Meeting: Salt Water Intrusion in Aquifers: Challenges and PerspectivesSOURCES OF SALINITY IN THE QUATERNARY SAND AQUIFER OF DAR-ES-SALAAM, TANZANIAMJEMAH, I.C. 1 ; MTONI, Y. 2 ; ELISANTE, E. 1 ; TUNGARAZA, C.T. 1 ; MTAKWA,P.W. 1 ; WALRAEVENS, K. 3ichikira@yahoo.com1. Sokoine University of Agriculture, Morogoro, Tanzania2. National Environment Management Council (NEMC), Dar es Salaam, Tanzania3. Laboratory for Applied Geology and Hydrogeology, Geological Institute, GhentUniversity, BelgiumP. Box 3038 Morogoro, TanzaniaAbstract. Groundwater first started to be used as a source of water supply for the Dar-es-Salaam City in 1943. However, many of the existing boreholes in Dar-es-Salaam were drilledin 1997 after Tanzania experienced a severe drought; since then groundwater use in the cityshows an increasing trend and currently over 50 percent of residents in Dar es Salaam Cityrelies on groundwater supply. Today, there are more than 10000 boreholes for domestic,water supply and industrial purposes. Demand and reliance on groundwater from a growingpopulation along the coast raises the need to increase efforts to protect and manage theresource. In the coastal aquifer of Dar-es-Salaam, groundwater quality is influenced byvarious potential sources of salinity that determine the composition of water extracted fromwells. The results show that the origin of salinity in the area is strongly influenced by:groundwater ascending from deep marine Miocene Spatangid Shales through faults,saltwater intrusion on the border of the Indian Ocean, and throughout, there is some salinitywithin the Quaternary aquifer, especially in intercalated deltaic clays in the fluviatiledeposits, showing some marine influences. Finally, also anthropogenic pollution mayincrease the groundwater salinity. For water points where water resistivity logs and VESwere available, the freshwater-saltwater interface depth ranges between approximately 7 mand 12 m. The dominant water type is mostly NaCl with pH < 7 in both aquifers (i.e. upperand lower) except for the shallow wells where CaHCO3 prevails with pH >= 7, andboreholes located near the Indian Ocean, where coral reef limestone deposits are located andthe water type evolves towards CaHCO3. In the lower aquifer, Cl- is higher than in the upperaquifer.Keywords: Tanzania; Dar-es-Salaam; Aquifer; Quaternary; Water type; Salinity251