American Journal of Water Resources, 2020, Vol. 8, No. 6, 246-255 Available online at http://pubs.sciepub.com/ajwr/8/6/1 Published by Science and Education Publishing DOI:10.12691/ajwr-8-6-1 Groundwater Quality Assessment in the Coastal Quaternary Sandy Aquifer in Darou Thiam-Ségoul Thioune-Fass Boye Axis (Niayes Area, Senegal) Alassane Thiam 1,* , Ousmane Coly Diouf 2 , Abdou Aziz Gning 1,2 , Issa Ndoye 1 1 Engineering Sciences Training and Research Unit, University of Thiès, Thiès, Sénégal 2 Faculty of Training for Ingeneering, University of Thiès, Thiès, Sénégal *Corresponding author: Received October 19, 2020; Revised November 20, 2020; Accepted November 29, 2020 Abstract 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 - , Ca 2+ , Mg 2+ , K + , SO 4 2- , HCO 3 - ) 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. Keywords: Niayes, groundwater, water quality, electrical conductivity, electrical resistivity tomography Cite This Article: Alassane Thiam, Ousmane Coly Diouf, Abdou Aziz Gning, and Issa Ndoye, “Groundwater Quality Assessment in the Coastal Quaternary Sandy Aquifer in Darou Thiam-Ségoul Thioune-Fass Boye Axis (Niayes Area, Senegal).” American Journal of Water Resources, vol. 8, no. 6 (2020): 246-255. doi: 10.12691/ajwr-8-6-1. 1. Introduction The “Niayes” area is the coastal zone located in the North-West of Senegal riding between four administrative regions: Dakar, Thiès, Louga and Saint-Louis. This region is strategic for the Senegalese economy of as it concentrates more than 80% of market gardening production (onions, potatoes, carrots, green cabbage, tomatoes, cherries, eggplants, lettuce and chili)., fruit and vegetables over a total area of 9,000 ha [1]. Its importance for Senegal is linked to their belonging to both the coastal domain and the continental domain [2]. This area, due to its geology and hydrogeology, is strategic in supplying drinking water to populations and in market gardening (onions, potatoes, carrots, green cabbage, tomatoes, cherries, eggplants, lettuce and chili). Water is the second limiting factor in these activities and undoubtedly the most essential. The drop in rainfall to which the Sahel had suffered obvious consequences on market gardening activity (onions, potatoes, carrots, green cabbage, tomatoes, cherries, eggplants, lettuce and chili) with the drying up of ponds and backwaters. This situation strained users to resort to groundwater resources located mainly in the Quaternary coastal sands to meet the many agricultural, industrial and mining needs. Numerous studies have focused on the hydrogeological characterization of this costal north sandy formation [1,3-12]. These various studies have shown that pumping rate from this sandy aquifer reached 21.547.317 m 3 in 2011 [13]. This pumping has led to a groundwater level decline and a tendency to pollution (nitrogenous, salty) threatening all market garden production [14]. Pesticide pollution is often noted in this agricultural area due to the leaching of organics and inorganics fertilizers used. Pesticides at concentrations greater than 0.1 μg/L (dicofol, chlorpyrifos and dimethoate) is also noted in places [15].