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The fresh-ground-water flow system of east-central Florida consists of a thin surficial sand aquifer underlain by the thick, highly productive carbonate rocks of the Floridan aquifer system. On the basis of permeability, this system is divided into the Upper and Lower Floridan aquifers, which are separated by a less permeable limestone sequence referred to as the middle semiconfining unit. The transmissivity of the Upper Floridan ranges from about 10,000 to 400,000 feet squared per day based on field aquifer tests, but simulation suggests an average value of 120,000 feet squared per day. The chemical quality of the water in the Upper Floridan aquifer varies according to proximity to recharge and discharge areas. Low concentrations of dissolved solids (less than 250 milligrams per liter) generally occur in recharge areas. However, in the discharge areas along the Atlantic Coast and along the St. Johns River, the dissolved-solids concentration is generally more than 1,000 milligrams per liter, and in places exceeds 25,000 milligrams per liter. The hydraulics of the Floridan aquifer system under predevelopment conditions involve mostly recharge to the Upper Floridan (by way of leakage from the surficial aquifer), lateral movement through the Upper Floridan for short distances, and discharge by waymore » of springs and seepage to streams. The imposition of pumping has altered the flow system, but not to a great degree. The simulated effects of 1978 pumpage (about 560 million gallons per day) on the predevelopment Floridan aquifer system flow regime are summarized.« less |
