Increasing population in southern Okaloosa and Walton Counties have resulted in regional declines in the potentiometric surface of the upper limestone of the Floridan aquifer. Water levels have declined as much as 160 feet since 1940, and during peak seasonal demand as much as 190 feet. The Pensacola clay confining bed inhibits interchange of water between the Floridan aquifer and the surficial sand-and-gravel aquifer. The latter aquifer is of secondary importance as a public supply source. The Bucatunna clay confining bed separates the Floridan into upper and lower limestone units; the Floridan is underlain by the relatively impermeable Lisbon/Tallahatta confining unit. The Floridan aquifer dips south to the Gulf of Mexico, and is recharged by rainfall in northern Okaloosa and Walton Counties and in Alabama. The regional gradient of the potentiometric surface of the upper limestone, and presumably that of the lower limstone also, is south. Pumpage was variable in 1978; from 10.9 to 19.0 million gallons per day in January and June, respectively. Saline water in the upper limestone of the Floridan aquifer is less than 10 milligrams per liter inland but may be more than 150 milligrams per liter along the coast. Lower limestone water may exceed 250 milligrams per liter chloride.
