Evaluation of Sea-Water Intrusion in Coastal Aquifers Using both Numerical Methods and Causal Research: A Case Study of Mombasa, Kenya

This research carried out in Mombasa Island links research done in 2020 on the effects of sea-water intrusion and the current state. The aquifer in Mombasa Island is semi-confined and consists of limestone and coral rock. Water samples were collected and tested from 32 boreholes to determine chemical qualities. Results showed that chloride levels ranged from 74 mg/l to 412 mg/l, with 34% of boreholes having high chloride concentration. After modelling using MT3D program results indicated that the boreholes near the ocean were interfered by sea-water intrusion because chloride concentration was high. Control measures to prevent further sea-water intrusion should be put in place. Therefore, from a practical point of view, individuals who have sunk boreholes since 2020 try to mitigate the problem by installing Reverse Osmosis systems within their facilities, to reduce chloride levels from borehole water. The current research analyses the impact of intrusion on the installed RO systems on Mombasa Island, including cost implications, with the view of proposing viable mitigation measures. The reverse osmosis system though expensive would save a lot of chloride entering the bore holes. It is a little bit expensive though but the end results are positive and the chloride levels will reduce the cost of using too much soap.