This edition of Eksplorium contains five (5) research articles from various fields. The first paper describes northern Sumatra's regional tectonic with titled “Tectonic Structures of Northern Sumatra Region Based on Seismic Tomography of P and S Wave Velocity.” The second paper is about the magmatic evolution of special volcanic features titled “Magmatic Evolution of Dago Volcano, West Java, Indonesia”. The third paper discusses groundwater pollution, titled “Characteristics of Nitrate Pollution in Shallow Groundwater on the South Slope of Mount Merapi, Yogyakarta, Indonesia”. The fourth paper is about the environmental impact of mining activities with titled “Prediction of Potential Acid Mine Drainage Formation in High Sulphidation Epithermal Deposit Using Geochemical and Mineralogy Approaches.” The last paper is about the laboratory research on fly ash for acid mine drainage, with titled “The Effect of Fly Ash Ratio Addition as Layering Material Using Free Draining Column Leach Test Method in Laboratory Scale.”