GEOPHYSICAL AND HYDROCHEMICAL APPROACH FOR SEAWATER INTRUSION IN NORTH SEMARANG, CENTRAL JAVA, INDONESIA

Abstract

Groundwater over exploitation leads to seawater intrusion in coastal area and influence the
quality of the groundwater aquifers. Geophysical and Hydrochemical investigations were carried out to
determine subsurface geologic formation and assessing seawater intrusion in Tanah Mas Residential area of
North Semarang, Indonesia. The seawater intrusion was investigated by 2D geoelectrical resistivity imaging
and generated using multi-electrode system with Wenner array configuration. Chemical analyses of
groundwater samples of indicated the range of salt concentrations meanwhile correlation of geophysical data
in the study area allows for the predictions of seawater-contaminated zones and their influence on in situ
salinity in the study area. The 12 geo-electrical sections were obtain up to penetration depth of about 27 m for
a total length of 150 m. The results of groundwater chemical testing indicated that there are three
groundwater samples with high levels of chloride ions. The three groundwater samples with high levels of
chloride ions are from wells F (434455, 9231239), J (434610, 9230204) and M (434117, 9231156). Seawater
intrusion in the study area were also detected and confirmed by the resistivity measurement. It can be
concluded that the seawater intrusion has reached the north, east and southern parts of the Tanah Mas
Residential area.