They mostly consist of unconsolidated sand enclosed by layers of limestone, sandstone or clay and the water is commonly extracted for urban use.
Some have been contaminated by saltwater, yet they provide most of the public freshwater supply southwest of Lake Okeechobee and along the Atlantic coast north of Palm Beach.
In surficial aquifers, the groundwater continuously moves along the hydraulic gradient from areas of recharge to streams and other places of discharge.
The aquifer lies close to the surface and is extremely vulnerable to pollutants that leach through the shallow limestone bedrock.
Over the years water levels have dropped due to water-well use by pumping, and it has been contaminated by industrial waste and saltwater intrusion.