The surficial aquifer in east-central St. Johns County, Florida

Water-Resources Investigations Report 81-14



The surficial aquifer, a composite of confined and unconfined water-bearing zones overlying the Miocene Hawthorn Formation, is an important source of water in St. Johns County, Fla. The water from wells open to the surficial aquifer generally meets quality standards recommended by the U.S. Environmental Protection Agency for public water supplies, except for concentrations of iron that for most wells are substantially greater than the recommended limit of 0.3 milligrams per liter. Data from 12 test wells drilled to the top of the Hawthorn formation, about 100 feet below land surface, indicate that the productive zones and confining beds in the surficial aquifer are discontinuous. Test well yields from individual zones range from less than 1 to 42 gallons per minute from depths between 20 and 100 feet below land surface. The most productive zones were generally found in the Tillman Ridge area, about 10 square miles in the west-central part of the area of investigation. Analysis of an aquifer test on a well in the Tillman Ridge area indicates a transmissivity of about 6,500 to 7,000 feet squared per day. The best local source of good quality water for development of a relatively large water supply is in the vicinity of Tillman Ridge. (USGS)

Additional publication details

Publication type Report
Publication Subtype USGS Numbered Series
Title The surficial aquifer in east-central St. Johns County, Florida
Series title Water-Resources Investigations Report
Series number 81-14
DOI 10.3133/wri8114
Year Published 1981
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Description v, 19 p.
Country United States
State Florida
County St. Johns County