Assessment of characteristics, water quality and groundwater vulnerability in Pakis District, East Java Province, Indonesia

Groundwater is a very important natural resource to support the activities of the residents of Pakis District, Malang Regency. On the other hand, increased activity puts pressure on groundwater quality. Agricultural intensification, urbanisation, and industrialisation can be sources of pollutants. Hydrological factors, topography, lithology, and surrounding rainfall are triggers for contamination of groundwater. The main objective of this research is to determine the characteristics, quality of groundwater, and its susceptibility to pollution. To complete this research, geoelectric measurements were carried out at 43 points spread throughout the study area and sampling of 18 shallow wells in agricultural, residential, and industrial areas for chemical analysis. All data obtained were analysed to create a map of the spatial distribution of groundwater vulnerability. The results show that the groundwater in the study location is in the transition zone and flows through the volcanic rock layers. The level of groundwater pollution is in the uncontaminated status to heavily polluted with pollutants in the form of heavy metal manganese and Escherichia coli bacteria. The spatial distribution of groundwater intrinsic vulnerability shows low, moderate, and high levels of vulnerability, respectively 32.99%, 60.87%, and 6.14% of the research area. Groundwater specific vulnerability associated with land use factors shows that 26.25% are negligible, 42.46% are low, and 31.29% are moderate. From this it can be concluded that the study area has been polluted both geogenically and anthropogenically, therefore, special actions must be taken to restore the quality of groundwater.