12 FLORIDA GEOLOGICAL SURVEY
Four wells in the Venice well field (21, 28, 25, and 26) tap only this aquifer.
The second artesian aquifer is separated from the underlying Floridan aquifer by a thick section of sandy limestone and dolomite, clayey sands, and clay. This section was estimated from a log of well 706-226-4 (fig. 2) to lie from about 130 to 270 feet below sea level. The section, as a unit, has a low vertical permeability but may contain beds whose horizontal permeability is relatively high. Beds of low permeability in this section confine water in the Floriday aquifer under pressure.
The Floridan aquifer consists of a large thickness of alternate layers of hard and soft limestone. These layers of limestone, so far as is known, act essentially as a hydrologic unit. The water in the Floridan aquifer at Venice is highly mineralized.
RECHARGE AND DISCHARGE
Ground water moves downgradient, from a high piezometric level to a low piezometric level. By mapping the piezometric surface in an aquifer the lateral direction of ground-water movement can be determined. By comparing the piezometric surfaces of aquifers above and below each other, the direction of interaquifer flow can be determined.
A statewide map of the piezometric surface of the Floridan aquifer shows that the water in the Floridan aquifer at Venice comes from the northeast outside of Sarasota County. No maps, however, are available for the piezometric surfaces of the overlying aquifers. A part of the recharge for the first and second artesian aquifers, however, probably comes from the area a few miles east of the Venice well field where the land surface is relatively high. The water-table aquifer, of course, is recharged locally by rainfall. The rate of recharge to the water-table aquifer is probably high because almost all the rainfall percolates downward or is evaporated rather than running off over the surface of the ground.
The water levels in most of the wells in the Venice well field were measured on July 12, 1962, 14 hours after pumping from the well field had ceased. The average elevation of the water level in test wells 1 and 2, which tap the water-table aquifer, was 7.6 feet above sea level. The average elevation of the water level in six wells (2, 5N, 5S, 12S, 13S, and 32), which tap the first artesian aquifer, was 8.1 feet; and the average elevation in three wells (21, 23, and 26), which tap only the second artesian aqtiifer, was 9.6