Groundwater Level Changes in the Coastal Construction Site of Coal-Fired Power Plant, Cilacap, Indonesia; Natural or Construction Effect?

The construction of power plant with the capacity of 1000 MW in the coastal area of Cilacap, Central Java, Indonesia, started from October 2017 until 2019. The construction is started by excavating the area at least 8 m of depth to build the foundation and underground cooling tunnel. During the dry season in 2018, community who live around the construction site reported groundwater level depletion in their wells. The power plant authority argued that groundwater extraction for shrimp ponds along the beach is also responsible for the groundwater level depletion in the region. This study aims to determine whether groundwater level declining in this area caused by natural conditions or due to construction activities. Field observations were carried out both in the rainy and dry seasons in 2019. It consisted of groundwater level measurement, resistivity measurement, and inventorying the utilization of groundwater. Groundwater modelling used to simulate the impact of groundwater extraction and construction of the power plant towards the groundwater flow around the construction site. The results suggested that seasonal difference within a year affects to the declining of groundwater level of 1.06 m by average at the community’s wells and the whole research area, while the dewatering practices by the power plant authority around the construction site of foundation and underground cooling tunnel were responsible to the declining of groundwater level of 1–2 m limited 500–700 m from the construction site.