Spatial Distribution of Seawater Intrusion Based on Various Lithologies in Pesanggaran Subdistrict, Banyuwangi, Indonesia

Seawater intrusion often occurs in shoreline areas closest to alluvium rock lithology and is caused by excessive groundwater exploration. In Pesanggaran Banyuwangi, saline groundwater was found at approximately 8000 m from the shoreline. Therefore, this study aimed to analyse the spatial distribution of seawater intrusion based on rock lithology, Electrical Conductivity (EC), and Total Dissolved Solids (TDS) in Pesanggaran, Banyuwangi. A descriptive-quantitative survey method was used to assess groundwater quality based on EC, TDS, and spatial distribution parameters. Interpolation with Inverse Distance Weighting (IDW) method was used to map seawater intrusion and its relationship to each parameter. The results showed that moderate-saline groundwater was found in several areas far from the coast with volcanic rock lithology, namely Kalibaru formations (Qpvk) and limestone lithology at Batuampar formation. Groundwater in shoreline areas (Alluvium) was dominated by freshwater due to the deposition process found in alluvium lithology, which could form an aquifer with high quantity. Saline groundwater in Batuampar and Kalibaru formations showed salt minerals flushing related to shallow marine deposition since the tertiary period. In conclusion, Pesanggaran Subdistrict had uneven spatial distribution, and no significant relationship with distance from the shoreline, but it was related to the deformation process for each lithology.