Seawater Influence on Groundwater in Pisang Island, Lampung

Pisang Island experiences population growth every year. The local community in this area uses groundwater for daily activities. Utilization was performed through pumping. Utilization has shown signs of negative impacts on the quality of groundwater, with the discovery of well water that tastes fresh and brackish. The purpose of this study is to analyze the parameter values to determine the processes involved in the formation of fresh, brackish/saline groundwater and to determine the level of influence of seawater on Pulau Pisang. Based on field studies including geological data, hydrogeology, groundwater flow patterns, electrical conductivity (EC), total dissolved solids, and pH values, 25 groundwater sampling points are determined. Laboratory testing was conducted on the samples for chemical analysis and the identification of their contents. The geoindicator method was used to assess the influence of seawater on groundwater, with several parameters including chloride (Cl) concentration and EC, Cl/Br ion ratio and Cl concentration, Na/Cl ratio, Ca/Mg and Ca/(HCO3 + SO4) ratios, Base Exchange Index (BEX) value, and trilinear pipe diagram. Based on the values of each parameter, there were three categories of groundwater characteristics: samples that were freshwater, samples influenced by seawater, and samples that were a mixture of freshwater and seawater.