Assessment of groundwater vulnerability and quality in coastal aquifers: a case study (Tipaza, North Algeria)

In the coastal aquifer of Nador, aquifer vulnerability index (AVI) and Groundwater occurrence, Aquifer hydraulic conductivity, Level above sea, Distance from the shore, Impact magnitude of the existing seawater intrusion in the area, Thickness of the aquifer which is being mapped (GALDIT) methods were employed to determine the groundwater vulnerability to anthropogenic pollution and seawater intrusion. The groundwater quality is also studied by using water quality index (WQI), for identify sectors with the best quality for drinking purposes. The AVI method classified the area into three vulnerability classes: low, moderate, and high vulnerability in the two parts of Nador valley due to anthropogenic activities, while the GALDIT method delineates the area into three vulnerability classes: low (<5), moderate (5-7.5), and high (>7.5) covering 47, 36, and 17 %, respectively, of the study area surface. The high class is located in the coastal sector; it is due to the proximity to the sea, the high hydraulic conductivity of aquifer, the exchange freshwaterseawater after the overexploitation, and also the thickness of the aquifer. WQI has been calculated in the present study to assess suitability of groundwater for drinking purposes. Twenty-four groundwater samples were collected from the Nador plain during the dry period of 2013. The WQI show that 17% of groundwater sample falls in good water category, 46 % falls in poor water category, 12 % falls in very poor water category, and 25 % falls in unsuitable water category. The groundwater unsuitable for drinking purposes is due to its high salinity, with high values of EC, Cl-, Na+, Mg2+, and SO42- due to the seawater intrusion.