Assessing the Impact of Seawater Intrusion on Groundwater Using Geo-indicators in Padang City

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 geo-indicators. 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 Geo-indicators 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. Based on the geo-indicator method, the level of seawater influence on groundwater in the study area is categorized into three categories: moderate influence, low influence, and unaffected. Moderate influence occurs in the southwestern part of the study area, which experiences a high increase in Cl concentration. Low influence occurs in the central and southeastern parts of the study area, while the coastal area and most of the study area are dominated by zones that are unaffected by seawater.