Saltwater intrusion is the movement of saline (or salty) water into an aquifer that previously held freshwater. If we know the source of the salt water is marine seawater, it is often referred to as seawater intrusion. Seawater intrusion occurs when an aquifer is connected to (outcrops into) a marine water body, and when the pressure in the aquifer falls low enough to allow the movement of saltwater into the aquifer. Areas immediately adjacent to marine shorelines are at the greatest risk for seawater intrusion.
Some aquifers have a higher susceptibility to seawater intrusion than others. Factors that increase an aquifer’s susceptibility include:
- Low amounts of water soaking into the ground
- High permeability of the aquifer formation
- Large groundwater withdrawals (pumping) from the aquifer
Although we cannot generally influence the permeability of an aquifer, we can (and do) influence the recharge area (impermeable surfaces) and pumping rates. Practices such as low impact development that allow water to soak into the ground, and water conservation can both aid in reducing the amount of seawater intrusion.