The Floridan aquifer within the area of investigation consists of 1,100 to 1,800 feet of soft, porous limestone interbedded with hard, dense limestone and dolomite overlain by several hundred feet of confining beds. From late 1948 to May 1972, water levels in wells tapping the Floridan aquifer declined as much as 14 feet in northern Clay and St. Johns Counties and more than 20 feet at Jacksonville in Duval County, Florida. These trends will probably continue as withdrawals from the aquifer increase. Water-level depressions exist at Green Cove Springs and Jacksonville because of natural discharge and large scale withdrawals. Withdrawals from wells could result in well interference unless the wells are spaced at least 1,000 ft apart. Two- to four-inch diameter wells drilled 100 ft or less into the aquifer yield 50 to 250 gal/min. Larger and deeper wells yield 1,000 gal/min or more. Hardness of water is generally less than 10 mg/liter. Quality of water from wells sampled over a span of 10 to 30 years has not changed noticeably. Principal recharge to the Floridan occurs southwest of the area in a lake region where rainfall percolates directly into the aquifer. (Woodard-USGS)
