This environmental impact assessment for the Korea Gas System Expansion Project describes anticipated negative environmental impacts and their mitigations. Terminal construction is expected to cause changes in the topography and the marine ecosystem, as well as cause impacts in air quality, seawater quality, and noise levels. Specifically, dredging works and site preparation will affect the marine environment and the natural topography. Tides, tidal discharge, current velocity, sedimentation, and marine species and quantity reduction of eggs, young fish, plankton, Benthos, and shellfish may result. Sewage discharged during construction and operation may affect seawater quality if disposed without treatment. Methods for reducing potentially harmful impacts include installing filters, scheduling work, installing dust barriers, and washing facilities for vehicles to mitigate air pollution. To prevent seawater pollution, install silt protectors to contain the production of suspended solids during land reclamation and dredging, operate sewage treatment systems, and provide an oil "fence" in the event of a spillage accident caused by a tank carrier. To decrease noise levels, construction vehicles will operate at low speed and nighttime work will be lomited during construction. After facilities are completed, a firefighting system will be installed in case of emergency.