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

This map shows the potentiometric surface of the Upper Floridan aquifer in the St. Johns River Water Management District and vicinity for September 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-foot contour intervals. The potentiometric surface ranged from 129 feet above sea level in Polk County to 77 feet below sea level in Nassau County. Water levels in most key wells ranged from 0 to 10 feet below in May 1987 levels in response to the lack of recharge from rainfall and an attendant increase in pumpage. Declines of about 0 to 3 feet from May 1987 levels were common in most areas of the district. However, the largest declines from May 1987 levels, as much as 7 to 10 feet, were mostly in well fields along the coastline. Many levels in the district were equal to or lower than the average levels of September 1986.