Saltwater intrusion is the movement of saline water into freshwater aquifers, which can lead to groundwater quality degradation, including drinking water sources, and other consequences. Saltwater intrusion can occur naturally in coastal aquifers due to the hydraulic connection between groundwater and seawater. Because saline water has a higher mineral content than freshwater, it is denser and has a higher water pressure. As a result, saltwater can push inland beneath the freshwater. In other topologies, submarine groundwater discharge can push fresh water into saltwater.
Groundwater extraction is the primary cause of saltwater intrusion. Groundwater is the main source of drinking water in many coastal areas of the United States, and extraction has increased over time. Under baseline conditions, the inland extent of saltwater is limited by higher pressure exerted by the freshwater column, owing to its higher elevation.
Saltwater intrusion has occurred to some degree in many of the coastal aquifers of the United States. Since saltwater cannot be used to irrigate crops or be consumed by people, saltwater intrusion can be very problematic to coastal communities that rely on fresh groundwater supplies for their livelihood. As sea levels rise along the coasts, saltwater can move onto the land, and storm surges or high tides can overtop areas low in elevation. It also occurs when saltwater infiltrates freshwater aquifers and raises the groundwater table below the soil surface.
There are a few strategies that can improve soil health and lessen the effects of saltwater intrusion in the short term. However, these are not long-term solutions. Farmers can remove excess salt from the soils through irrigation. Natural rainfall events will also help with this process. Farmers can also add gypsum to decrease excess salt in the soil and use compost and manure products with low salt levels.
To help farmers and landowners adapt to saltwater intrusion, researchers can track salinity changes over time in groundwater wells and surface water to develop a better picture of which areas are most vulnerable. Improved understanding of the problem can help in developing long-term solutions.
Saltwater intrusion can result in the need for water utilities to increase treatment, relocate water intakes, or develop alternate sources of fresh water. EPA works with drinking water utilities to provide clean and safe drinking water. Source water quality, both groundwater and surface water, is at risk from saltwater intrusion due to rising sea levels, changing water demands, and the occurrence of drought.
