Water has an important role in creating pollution problems in the mining regimes influencing the surrounding surface
environment. The purpose of this study is to make an assessment of groundwater quality in an underground mine site in
Portugal with a view of determining the pollution potential of groundwater. In the corresponding surface area of this
underground mine, intersections of four faults form rock blocks which delimit the surface subsidence influencing the
flow pattern of the surface streams and the groundwater table resulting in inflow of groundwater and rainwater into
mining excavations. When this water comes into contact with the virgin rock mass containing pyrites in presence of
atmospheric air, acid mine water is formed. This acidic water reacts with the broken rock material dissolving metallic
sulphides into solution and also carrying suspended solids. When discharged in the “Boldehão” River, these waters
produce diverse environmental impact levels such as pH low and Zn high levels risk cause for irrigation, pH, Cu, Fe and
Mn high level risk for consumption human, and pH, Cu and Zn cause high level for fishes.