Potentiometric surface of the upper Floridan Aquifer in the St. Johns River Water Management District and vicinity, Florida, May 1988

This map shows the potentiometric surface of the Upper Floridan aquifer in the St. Johns River Water Management District and vicinity, for May 1988. The Upper Floridan aquifer is the principal source of potable water in the area. Water level measurements were made on approximately 1,000 wells and on several springs. The potentiometric surface is shown mostly by 5-foot contour intervals. In the Fernandina Beach area of Nassau County, a 30-foot interval is used to show a deep cone of depression. The potentiometric surface ranged from 127 ft above sea level in Polk County to 79 ft below sea level in Nassau County. Water levels in many key wells were about the May average. Most levels in the district were below the levels of May 1987. Declines of about a foot or less from May 1987 levels were common along the coast, but inland, the potentiometric surface declined as much as 2 to 6 ft in places.