The primary sources of water in the area are from the surficial and Floridan aquifers. The surficial aquifer, consisting of thin permeable zones of sand, shell, and limestone, provides limited water supplies (10-50 gallons per minute). Its estimated transmissivity ranges from less than 100 to 10,000 feet squared per day. Its water is generally of acceptable quality for most uses, except near the coast. The Floridan aquifer consists of three zones of permeable limestone and dolomite separated by semiconfining beds of hard, massive dolomite and limestone, all of which are confined by leaky confining beds. The upper and middle zones, about 530-1,000 feet and 1,200-1,700 feet below land surface, respectively, have transmissivities ranging from 20,000-50,000 and 40,000-60,000 feet squared per day, respectively. The lower zone, about 2,000-2,100 feet below land surface contains very saline water. Water in the upper zone contains chloride concentrations generally ranging from 20-40 milligrams per liter. In Fernandina Beach, water from a few wells tapping this zone has relatively high chloride concentrations (190 milligrams per liter), probably due to upward migration of saline water from deeper zones through uncased or improperly-plugged well bores and not by lateral intrusion. (USGS)