Potentiometric surface of the upper Floridan Aquifer in the St. Johns River Water Management District and vicinity, Florida, September 1984

This map shows the potentiometric surface of the Upper Floridan aquifer in the St. Johns River Water Management District and vicinity for September 1984. 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 40-foot interval is used to show a deep cone of depression. The potentiometric surface ranged from 130 feet above sea level in Polk County to 83 feet below sea level in Nassau County. Water levels in key wells ranged from slightly above average to several feet below average for September in response to diverse area rainfall patterns. Most levels in the district were about the same as the levels of September 1983. However, in Nassau County levels were generally below those of September 1983, and levels in Volusia County were mostly higher than September 1983 levels. (USGS)