Abstract
Groundwater is water that is found below the ground surface or in rock layers. Seawater intrusion is a problem caused by excessive groundwater extraction which often occurs in coastal areas. Rembang is an area located in the coastal area. Rembang Regency has the potential for seawater intrusion. The impact of seawater intrusion can affect economic, social and cultural development in coastal areas as well as the quantity and quality of groundwater. The purpose of this study is to determine areas that have potential for seawater intrusion in the study area. The methods were geological mapping, groundwater quality analysis, GALDIT approach and its validation using TDS, DHL and Chloride. The interpretation of the area that has the potential for seawater intrusion is carried out with validation in the research area. The results conducted that in the research area consists of limestone, sandstone, claystone, the presence of porphyry andesite and alluvium. Based on the analysis of the vulnerability of seawater intrusion using the GALDIT method, it was found that there are 3 levels of vulnerability, namely middle to very high vulnerability. High vulnerability has GALDIT index > 7.5, located on the north coast of Rembang and Kaliori sub-districts.. The high vulnerable is 5-7.5, located mostly in Kaliori and Rembang sub-districts, and a little in Sulang, Sumber, Bulu, and Gunem sub-districts. The middle vulnerable is in the range of 2.5-5 mostly in Bulu, Gunem, Sumber, Sulang sub-districts, and a little in Rembang and Kaliori sub-districts. The validation carried out has a high match in the north of the study area. The very high level of vulnerability is in accordance with the distribution of the population and the land use map where the Kaliori and Rembang sub-districts have a large population and the land use is filled with buildings and settlements.