238 



The long-term water-quality impacts that the higher stands of the 

 sea have had on the Floridan Aquifer are still evident in a large part of 

 the aquifer, particularly where it is confined and occurs at depth. Salt 

 water occurs in the Floridan Aquifer in south Florida, along the east coast 

 of Florida to just south of St. Augustine and in the St. Johns River 

 valley, and along the west coast northward almost to Tampa Bay 

 (Stringfield, 1966). This water appears to be seawater that has not been 

 flushed from the aquifer. Some of it is connate (formation) water, but 

 some of it entered the aquifer during higher stands of the sea during 

 Pleistocene time. In southwestern Florida, dissolved solids in the aquifer 

 increase downgradient , and the general flow pattern in the aquifer is that 

 of flow toward the south and west that has been gradually improving 

 groundwater quality farther and farther downgradient in the aquifer since 

 the last period of marine inundation (Steinkampf, 1982). 



Saltwater- Freshwater Interface Location . The location of the 

 saltwater- freshwater interface in the Floridan Aquifer apparently 

 represents an approximate equilibrium between the existing piezometric 

 heads in the aquifer, aquifer flow rates, and discharges to the sea. In 

 the Floridan Aquifer in northeast Florida, piezometric heads in the aquifer 

 are still above sea level at the coastline and eastward beneath the 

 Atlantic Ocean, and the saltwater -freshwater interface is inferred to 

 extend eastward more than 70 miles beneath the Atlantic Ocean (Brown, 

 1984) . In west-central Florida, the intersection of the interface with the 

 top of the Floridan Aquifer probably occurs offshore, and the intersection 

 of the toe of the interface with the bottom of the aquifer probably ranges 

 from a few miles to about 20 miles inland from the coastline (Wilson and 

 Gerhart, 1982). 



In the Miami area, the Biscayne Aquifer is unconfined, and the 

 saltwater- freshwater interface occurs near the coastline, where piezometric 

 heads in the aquifer are at or near sea level. The interface in the 

 Biscayne Aquifer consists of a broad zone of transition that is probably 

 about 2000 ft wide at the base of the aquifer (Cooper, 1964). Saltwater 

 intrusion has occurred inland from the coast and along tidal streams and 

 canals that have lowered groundwater levels by means of excessive drainage 

 and improperly placed control structures (Klein and Hull, 1978). 



