Potentiometric surface of the upper Floridan Aquifer in the St. Johns River Water Management District and vicinity, Florida, May 1987

The potentiometric surface of the Upper Floridan aquifer in the St. Johns River Water Management District and vicinity is shown for May 1987. 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-ft contour intervals. In the Fernandina Beach area of Nassau County, a 30-ft interval is used to show a deep cone of depression. The potentiometric surface ranged from 129 ft above sea level in Polk County to 54 ft below sea level in Nassau County. Water levels in key wells ranged from several ft above to several ft below the May average in response to areal patterns of rainfall. Most levels in the district were above the below average levels of May 1986. Rises of about 2 ft from May 1986 levels were common in the southern half of the District, and the potentiometric surface rose as much as 6 to 8 ft in places. (USGS)