Risk Analysis of the Groundwater Pollution in Sidoarjo Regency Based on Groundwater Quality Test and Vulnerability Mapping

— Mining and oil and gas industry were prevalent recently. However, the impact of the mining and oil and gas industry can affect the environment. One of the effects is the decrease in water quality. Another example of misconduct in the oil and gas industry is Lapindo mudflow. This mudflow has been flown out since 27 May 2006. This accident damaged infrastructure around the area and the mudflow already sink 600 ha of land and residential areas. This problem continues today, and nobody knows where it comes to an end. In this study, our outcome is to know the safety of the water resources around the mudflow area. The objective of this study is to know the distribution pattern of the pollutant and health risk analysis of the people around the mudflow area. To know the health risk of the Lapindo mudflow, vulnerability map has been made based on the DRASTIC Index method. Also, Pollution Index method was needed to assess the risk analysis accurately. Besides that, in this study, simulation of the pollutant transport across the surrounding area has been simulated by using advection theory in Hydrus-1D. The potential of groundwater vulnerability was calculated using DRASTIC Index method. The result of the calculation was conformable with the outcome of the water quality test using Pollution Index method. The result of the DRASTIC index showed that the level of groundwater vulnerability is medium. Then, the result of water quality test revealed that the water from water wells is to meet quality standards and moderately polluted. The assessment of health risk analysis showed that the water is not detrimental to health. On the other hand, the simulation result for Fe, Al, and Mn have a similar speed to reach DK1 water wells, which is 1760,6 meter from the center of the mudflow. All three pollutants take ± 8 years to reach DK1 water wells. The conclusion of this study is the water wells, which is used by local people, was not detrimental to health, and Hydrus-1D was able to simulate the distribution of pollutants in the affected area.