Assessing the Impact of Seawater Intrusion on Groundwater Using Geoindicators in Padang City
Vito Charly (a,b), Heru Hendrayana (a), and Costandji Nait (b)

a) Departement of Geological Engineering Gadjah Mada University, Yogyakarta, Indonesia
b) Ministry of Public Works and Housing of Indonesia, South Jakarta, Indonesia

Abstract

Padang City is the capital of West Sumatra Province. The geographical condition of Padang City is directly adjacent to the sea. One of the direct negative impacts is the potential for seawater intrusion. Seawater intrusion is a groundwater problem in coastal areas. Based on this, this research was carried out to map groundwater vulnerability zones to seawater intrusion. The method used to determine the zoning of seawater influence distribution is analyzed based on Electrical Conductivity (EC) values and geoindicators. Analysis of EC values from 54 groundwater samples revealed that 2 samples were classified as moderately saline, and 1 sample was classified as slightly saline. From the groundwater ion values, two of the three samples showed chloride values >400 mg/L. The comparison of the Cl/HCO3- ratio shows that the 2 samples each have a medium and high influence on seawater. The results of the analysis using Geoindicators with 6 parameters-Increased Ca concentration, Cl/Br Ratio, Na/Cl Ratio, Ca Enrichment, Simpson Ratio, and BEX-indicate the level of vulnerability to seawater. It shows that 2 samples, SG-13 and SG-15, are moderately influenced- 9 samples are low influenced, and the remaining 16 samples are uninfluenced.

Keywords: geoindicators, electrical conductivity, groundwater

Topic: Hydrology, hydrogeology, and geology engineering