THREE-DIMENSIONAL NUMERICAL SIMULATION OF FRESH WATER INJECTION AND SALT WATER EXTRACTION SCHEMES TO PREVENT SEAWATER INTRUSION IN A LAYERED COASTAL AQUIFER SYSTEM DUE TO GROUNDWATER PUMPING

A series of three-dimensional numerical simulations is performed to evaluate the fresh water injection and salt water extraction schemes for preventing seawater intrusion in a layered coastal aquifer system due to groundwater pumping using a multidimensional hydrodynamic dispersion numerical model. The layered aquifer system is composed of a clay layer underlain by a sand layer on a bedrock. It is the typical hydrogeological setting of the western coastal aquifers in Korea. In the numerical simulations of the fresh water injection scheme, the amount of fresh water injection, the number of injection wells, the horizontal location of injection wells, and the vertical interval of fresh water injection are considered to determine an optimal fresh water injection scheme. Similarly, in the numerical simulations of the salt water extraction scheme, the amount of salt water extraction, the number of extraction wells, the horizontal location of extraction wells, and the vertical interval of salt water extraction are considered to determine an optimal salt water extraction scheme. The results of the numerical simulations of the fresh water injection scheme show that the seawater intrusion is best prevented when the amount of fresh water injection is 30% of the groundwater pumping amount from a fully penetrating single injection well, which is located closer to the pumping well than the coastal line. On the other hand, the results of the numerical simulations of the salt water extraction scheme show that the seawater intrusion is best prevented when the amount of salt water extraction is 30% of the groundwater pumping amount from a fully penetrating single extraction well, which is located in the middle of the pumping well and the coastal line.