AQUIFER CHARACTERIZATION AND EVALUATION OF SEA WATER INTRUSION USING HYDROGEOCHEMICAL ANALYSES FOR MALEKULA, VANUATU

This study examined the aquifer characteristics and risk of salt-water intrusion on the island of Malekula, Vanuatu. Data were collected from 14 groundwater samples from various wells. Water parameters including pH, TDS, DO, and temperature were taken in the field. Samples were analyzed using ICP-MS, ion chromatography, and bicarbonate titrations to determine anion and cation concentrations in each sample. From these analyses, Piper and Stiff diagrams were created to determine aquifer connectivity on the island. Sea-level rise projections were used to model the salt-water interface for 2020, 2035, 2050, and 2100. Results from the hydro-chemical analysis showed that there are 5-7 different aquifers present from the sample locations, including one perched aquifer. Some samples contained high levels of sodium and chloride ions (up to 572 mg/L), indicating a small extent of salt-water intrusion. Due to the predicted effect of sea-level rise on the salt-water interface, inland well relocation is recommended. A water treatment facility is also recommended due to the presence of coliform bacteria in 5 of the 15 groundwater samples.