Alassane Thiam^1,, Ousmane Coly Diouf², Abdou Aziz Gning^{1, 2}, Issa Ndoye¹

The “Niayes” area plays a major role in the Senegalese economy due to a very high market garden production. This “Niayes” area produces almost all of Senegal's vegetables (onions, potatoes, carrots, green cabbage, tomatoes, cherries, eggplants, lettuce and chili). Water supply to meet irrigation needs in this area comes mainly from groundwater resources. This Groundwater pumping has harmful consequences on the behavior on the groundwater piezometric level drop. Since 1987, the piezometric dome observed in this aquifer experienced a water level drop of 2.5 m at Taїba and Tawa Fall areas. The electrical resistivity tomography (ERT) shows the presence of a saturated and an unsaturated zones in the presence of dry sandy dunes with a thickness of about 12 m resting on a saturated zone corresponding to the aquifer captured by the 2 boreholes and the piezometer. Chemical analyzes showed an Electrical Conductivity values equal respectively to 269, 470 and 1110 µS/cm at Fass Boye piezometry, Darou Thiam and Ségoul Thioune wells. Electrical Conductivity value of 1110 µS/cm indicates a strong groundwater mineralization. This mineralization is correlated with Na⁺ concentration of (145 mg/L) close to pollution by salt resulting in salinization of water making them unsuitable for consumption and irrigation. Water samples at Fass Boye piezometer and Ségoul Thioune well show low to medium mineralization because the electrical conductivities are respectively in the order of 269 and 470 µS/cm. Majors ions concentration (Cl^-, Ca²⁺, Mg²⁺, K⁺, SO₄^2-, HCO₃^-) with respective maximum concentrations of 140.84; 48; 21.32; 8.81; 78 and 122 mg/L, meet all World Health Organization standards for drinking water. Applying the Piper diagram to these groundwater samples shows a sodium and potassium chloride facies associated with proximity to the sea.

Niayes, groundwater, water quality, electrical conductivity, electrical resistivity tomography