TIMING AND GROUND WATER CIRCULATION WITHIN THE FLORIDAN AQUIFER SYSTEM OF SOUTH FLORIDA

Synthesis of recently acquired geochemical and hydrogeologic data provides fresh insight into existing theories on the timing and development of groundwater circulation within the Floridan aquifer system in south Florida. Groundwater samples were collected from the Floridan aquifer system, south of Lake Okeechobee for analysis of stable isotopes of water, dissolved noble gases, salinity, and radiocarbon. In addition, present day, water temperature and potentiometric head data were obtained and mapped for the region.

Freshwater derived from precipitation circulates in the upper Floridan aquifer with increased salinities down gradient and near the coasts. Noble gases, reflecting temperature at recharge, and radiocarbon data indicate recharge and groundwater flow have occurred over the past 25,000 years. Along the southeast coast, however, temperature and salinity data are more indicative of relict lateral seawater intrusion or upward recharge from the lower Floridan aquifer.

Noble gas recharge temperatures and the stable isotopes from the lower Floridan aquifer are identical to modern sea water (<400 m) from the Florida Straits, indicating that saline water recharged the lower Floridan aquifer after the end of the last glacial period when sea level returned to its present height. Thus, the movement of seawater within the lower Florida aquifer is less than 10,000 years. Present date temperature, potentiometric heads and groundwater model simulations indicate that cyclic ground water flow occurs only along the southeast coast of Florida, with groundwater flow in the lower Floridan aquifer towards the southeast. In the central part of south Florida, the upper Floridan aquifer recharges the lower Floridan aquifer via downward leakage.