Evaluation of Saline Water Intrusion and Suitability of Groundwater for Domestic Purposes in Lagos Coastal Area, SW Nigeria: Using NIOMR Jetty as a Case Study

The current study deals with the evaluation of groundwater suitability for domestic purposes within the coastal communities of Lagos, using a 200 feet monitoring borehole at the Nigerian Institute of Oceanography and marine research (NIOMR) Jetty, Southwest Nigeria as a case study. The monitoring borehole water was analysed for physicochemical parameters (pH, electrical conductivity, salinity, dissolved oxygen, temperature) and nutrients (nitrite, nitrate, phosphate, sulphate) from January-December, 2019. A borehole located in the Lagos mainland was used as control. The analytical results showed that the concentration ranges of nitrite (3-7 mg/L), nitrate (16-32 mg/L), salinity (13.99-21.18‰) and electrical conductivity (2545-3072 μS/cm) exceed the permissible limit stipulated by the United State Environmental Protection Agency (USEPA), which are 1 mg/l, 10 mg/L, 0‰ and < 1500 μS/cm for nitrite, nitrate, salinity, and electrical conductivity respectively. The groundwater samples from the control station showed electrical conductivity and salinity ranges of 7.3-73 μS/cm and 0‰ respectively, and which made samples from the control to be classified as freshwater. The high salinity (21.18‰) and electrical conductivity (3072 μS/cm) during the wet season (July, September and October) affirmed the influence of seawater intrusion into the freshwater aquifer of the monitoring borehole. Our study further showed the highest elevated groundwater level (1.58 m) in October, which coincides with the highest electrical conductivity (3072 μS/cm) value in the same month. While the correlation between the groundwater level and electrical conductivity clearly shows evidence of seawater intrusion at the study location, elevated nitrite and nitrate concentrations above the USEPA permissible limits, provide evidence for leachate of seepages from anthropogenic sources. This study has shown not only that subsurface pollutants in the form of saline water intrusion and infiltration of leachates are the major controlling factors of groundwater pollution at the NIOMR Jetty, but it has also revealed an essential insight into the groundwater pollution of the coastal environment of Lagos state, Southwest Nigeria.