Saltwater Intrusion Puts Drinking Water at Risk

U.S. coastal counties depend on groundwater for 18% of their fresh, potable water. This groundwater is at risk from an increasing coastal population and coastal storms.

Population pressures in coastal Georgia – saltwater intrusion below the surface (Figure 1)
Nearly all coastal aquifers around the world experience some form of naturally occuring saltwater intrusion (Johnson, 2007).  However, when an aquifer is pumped faster than it is replenished, it causes saltwater to intrude the aquifer. The Upper Floridan aquifer lies beneath portions of coastal South Carolina, Georgia, and northern Florida and is the primary source of freshwater for 24 counties in coastal Georgia.  The aquifer has been used extensively since it was first pumped in the 1800s and faces increasing demand from Georgia’s rapidly growing coastal population. Withdrawals from the aquifer to support public supply, industry and irrigation have resulted in groundwater declines in the coastal zone, and consequent salt water intrusion in Brunswick, Georgia. This contamination has created competing demands for the remaining freshwater and has further restricted use of the Upper Floridan aquifer (Barlow, 2003).

Coastal storm surge in St. Tammany Parish, Louisiana – saltwater intrusion at the surface (Figure 2)
Coastal aquifers are also vulnerable to saltwater flooding due to storm surge and sea level rise.  St. Tammany Parish is located on the northern shore of Lake Pontchartrain in Louisiana and has a rapidly growing population.  Underlying St. Tammany Parish is the Southern Hill Aquifer System, a sole-source aquifer system supplying the Parish with the majority of its freshwater (Van Biersel, 2007).  After coastal storm surges from Hurricanes Katrina and Rita blanketed much of the area, it was found that saltwater intruded portions of the shallow aquifer through many of the wells along Lake Pontchartrain's shoreline (Tomaszewski and Lovelace, 2005).

Fig. 1. Intrusion below the surface.                    Fig. 2. Intrusion at the surface.
Georgia groundwater                   Georgia groundwater

Source: Barlow, et al. 2009 (Figure 1); Tomaszewski and Lovelace, 2005 (Figure 2)

Sampling for deep saltwater intrusion in Glynn County, Georgia.
Sampling for deep saltwater intrusion in the Upper Floridan aquifer in Glynn County, Georgia. Credit: Alan Cressler

For more information:

Saltwater Intrusion in the Coastal Regions of North America.

Science and the Storms: the USGS Response to the Hurricanes of 2005

Closer Look

Relevant Links

U.S. Geological Survey Water Use in the United States
http://water.usgs.gov/watuse/