Potentiometric surface of the Floridan aquifer in the St. Johns River Water Management District and vicinity, Florida, September 1981

This map presents the potentiometric surface of the Floridan acquifer in the St. Johns River Water Management District and vicinity for September 1981. The Floridan acquifer 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 20- and 40-foot intervals are used to show a deep cone of depression. The potentiometric surface ranged from 134 feet above NGVD (National Geodetic Vertical Datum of 1929) in Polk County to 90 feet below NGVD in Nassau County. Record low water levels for September were recorded in many counties due to lack of rainfall. September 1981 levels were as much as 10 feet and commonly 2 to 3 feet lower than the below normal September 1980 levels. Water levels rose from September 1980 levels on the coastline at St. Augustine and from Flagler Beach south to New Smyrna Beach.