Teknik-teknik geoelektrik dalam Pemetaan air masin di Kuala Selangor

Vertical electrical sounding and resistivity imaging techniques are used to map the salinity distribution of the . groundwater near the coastal area of Kuala Selangor. This survey is carried out in conjunction with the groundwater drilling of the alluvium aquifer by the Mineral and Geoscience Department. Geochemical analysis data shows that the salinity of the pumped water varies with different locality. Areas closer to the coast and river show higher salinity while samples taken from areas towards the inland are lower in salinity. The high groundwater salinity in some areas is believed to be due to either saltwater intrusion from the nearby sea or river infiltration during tide season. Thickness of aquifer varies from 20 to 30 metres and it consists of sand and gravel mixed with clay lenses. This aquifer is lying on top of metasediment and granite bedrocks and overlain by approximately 15 metres of yellowish brown hard clay with sand and silt lenses. Electrical surveys are carried out in the monitoring area in order to map the groundwater salinity distribution of the whole area. Vertical electrical sounding with Schlumberger electrode array and lateral-vertical imaging technique are used throughout the mapping. In the vertical electrical sounding technique, maximum current electrode spacing used is 300 metres. Wenner electrode configuration system is applied in the electrical imaging survey. Only 4 electrodes are used in the vertical electrical sounding while 50 electrodes connected by a multicore cable is employed for the electrical imaging. ABEM SAS 300C resistivity meter is used for potential measurement and selection of potential and current electrodes is made by a switch box. Maximum electrode spacing used in electrical imaging is 200 metres. Chemical analysis data of the groundwater samples will be used as a supplementary information in the interpretation. Vertical electrical sounding measurement is made at 45 stations along three main roads across the survey area in a direction perpendicular to the coast. Distance between each station is about ~-2 kilometres and the total length of the survey lines are about 60 kilometres. Vertical electrical sounding results show that the groundwater in the area 320 SITI ZALiPAH JUMARY, UMAR HAMZAH, ABDUL RAHIM SAMSUDIN & EDNA PillS MALIM can be divided into fresh, brackish and saline and the boundaries between brackish and saline is along 4-8 kilometres from the coastal line. This result is in agreement with the mapping of the chloride zones through underground water sampling. Boundaries of fresh-brackish and brackish-saline zones are also detected in the electrical imaging results at several selected localities determined from the previous sounding and chloride analysis.