Groundwater pollution by nitrate has become serious environmental issues in the Shirasu plateau of Kasanohara of Osumi peninsula, Kagoshima prefecture, Japan. We developed three-dimensional numerical simulation model to understand how the pollution diffused in the aquifer of the plateau. To evaluate the effects of countermeasures for the pollution source, the model was also used to simulate remediation stage. The numerical results showed that the nitrate concentration in the springwater from the edge of the plateau is very low. Therefore, the countermeasure against a contaminant source will be effective. Accourding to the results of the remediation simulation, it will take around 8 years to show the large effects of countermeasures of 80% reduction in nitrate concentration of the source zone. Even if the 50% reduction case, the nitrate concentration in the springwater reduced around half of the initial concentration after about 8 years.
