Definition - What does Saltwater Intrusion mean?
Saltwater intrusion is the movement of saline water into freshwater aquifers, which can cause contamination of fresh drinking water sources in a region and other problems. This problem occurs naturally in aquifers that are in coastal areas due to the hydraulic connection between ground and sea water, which happens underneath the surface of the earth.
Safeopedia explains Saltwater Intrusion
Saltwater intrusion happens when there are two different densities in the fresh water aquifer and the saltwater from the sea and this allows the ocean's water to intrude into the fresh water aquifer through the ground. This usually happens where a coastal freshwater aquifer is supporting a large population and the withdrawal from this water source is greater than its replenishment.