Publication Details

GROUNDWATER QUALITY ASSESSMENT IN SMALL ISLAND AQUIFER, MABUL ISLAND, SABAH

Mabul Island depend mostly on groundwater as a major source of water supply for domestic and tourism industry purposes. There was no inflow from river and the highest level was 4.2 meter above mean sea level. Rainwater is the only source of recharging the groundwater to sustain the quality. Over-abstraction of fresh groundwater lens leads to saltwater intrusion and deterioration of its quality. This study aimed to assess and understand the groundwater characteristics in the fragile aquifer of the island. In order to assess this issues, a groundwater sampling was collected 4 times between March 2018 to October 2019 from 15 dug wells scatter in the island. The geochemistry concentration of chloride and electrical conductivity usually used to determine saltwater intrusion. This study focuses on the assessment of freshwater lens mixing and salinization. The mixing fresh groundwater lens situated from 2.5 to 2.9meter depth below ground level (bgl) which quality defer from 1,218 to 23,170 µS. Depth below than 4 meter from ground level is considered as seawater. Most of the groundwater pumping wells came from the tourism industry and were not used for a drinking purposes. Most of the groundwater was identified as saline water and only a part of the island shows slightly saline water based on the ionic strength and chloride concentration. Based on the analysis of groundwater lens quality and density dependent flow model indicate that the island’s coastal aquifer has been encroached by seawater. Extensive research is currently being carried out worldwide in order to understand the mechanisms of SI and develop strategies to control the process. For example, costly technological solutions, such as desalination, barriers or injection wells have been implemented to deal with the reduction in freshwater availability. Consideration for this technologies factor affecting saltwater and freshwater interface.