Application of GOD Method to Identify the Groundwater Vulnerability to Pollution in the Sub-District of West Limboto, Gorontalo Regency, Indonesia

Population increment, and agricultural sector expansion in West Limboto, Gorontalo Regency, Indonesia, affect waste or pollutant increase. The community uses shallow groundwater as the main water source. Since shallow groundwater is vulnerable to pollution due to its depth and community activity, this study aims to identify its vulnerability in West Limboto. It was identified using the Groundwater Confinement, Overlying Strata, and Depth to Groundwater (GOD) Method. Those are also the parameters to be considered. The first parameter needs the aquifer-type data; the more unconfined the aquifer, the higher the index value. The second parameter needs the lithology data covering the stratigraphic aquifer, which is the high permeability lithology will have a higher index value. In comparison, the third parameter needs groundwater table data, which is the nearest to the ground surface, the higher the index value. The analysis shows that the Groundwater Vulnerability Index in the southern part of the study area is 0.5 – 0.7. It means that the aquifer is highly vulnerable to many pollutants. While at the middle to the northern part of the study area have an index of groundwater vulnerability in the range of 0.1 – 0.3, which means that the aquifer is vulnerable to conservative pollutants only. Therefore, the groundwater vulnerability of the study area was classified into 2 classes, the high index was in the southern part, and the low index was in the middle to the northern part of the study area.