Potentiometric surface map of the Floridan aquifer in the St. Johns River Water Management District and vicinity, Florida, May 1979

This map presents the potentiometric surface of the Floridan aquifer in the St. Johns River Water Management District and vicinity for May 1979. The Floridan aquifer is the principal source of potable water in the area. Water-level measurements were made on approximately 1200 wells and on several springs. The potentiometric surface is shown by 5-foot contour intervals except in the Fernandina Beach area where 20-foot intervals are used to show a deep cone of depression. This is the fourth map of a series covering the entire St. Johns River Water Management District and vicinity. Two maps cover the low water-level period in May and two show the high-water period in September. The potentiometric surface ranged from 125 feet above the National Vertical Datum of 1929 (NGVD) in Polk County to 120 feet below NGVD in Nassau County. (USGS)