"U.S. Geological Survey report documents underground movement of salt water."
"It’s a gentle intruder, moving stealthily underground, out of sight but not undetected. Salt water continues to move farther inland in Florida’s Miami-Dade County, albeit at a slower rate, according to new U.S. Geological Survey mapping.
Researchers and water managers in southern Florida keep a wary eye on the ocean’s landward thrust because of the region’s precarious freshwater balance. All of Miami-Dade County’s municipal water, which serves several million residents and visitors, comes from groundwater, primarily from a thin lens of fresh water called the Biscayne Aquifer.
Rising seas are a visible threat to coastal areas. But the danger above is mirrored below in the form of rising salt concentrations in many coastal aquifers. In Miami-Dade County, the USGS study mapped the boundary where salt water meets the base of the Biscayne. Because it is less dense, fresh water sits on top of the saltwater wedge, which is thickest near the coast and thinner inland."
Advertisement 
