24 FLORIDA GEOLOGICAL SURVEY
HEAD AT BASE OF SALT-WATER WEDGE
The head at the base of the salt-water wedge was determined from the relationship between salt water and fresh water. The bottom of the water-table aquifer is about 18 feet below sea level (fig. 4). The specific gravity of sea water is about 1.025 and the specific gravity of fresh water is about 1.00. A column of sea water, therefore, 18 feet high has the same weight as a column of fresh water 18.45 feet high (18 x 1.025). Thus, the head at the base of the salt-water wedge is equivalent to that of a column of fresh water extending 0.45 foot above sea level.
PUMPING LEVEL OF PIEZOMETRIC SURFACE
The drawdown due to the pumping of water from the Venice well field was computed by the use of the coefficients of transmissibility and of leakage that were determined from the pumping tests. Before computing the drawdowns, however, the nonpumping or the design level of the piezometric surface must be determined. These drawdowns will be subtracted from the design level of the piezometric surface in order to determine the pumping level.
Design piezometric &urface: The nonpumping piezometric surface, of course, fluctuates so that there is no fixed level from which the drawdowns should be subtracted. For the purposes of this analysis, the level of the piezometric surface during a period when the piezometric surface is low will be used. This level, referred to in this report as the design piezometric surface, is the average level of the nonpumping piezometric surface during a period of a few days or weeks when the surface is at its lowest.
If a record of the fluctuations of the piezometric surface were available over a sufficiently long period, the design piezometric surface could be established from the record. Unfortunately, only one set of measurements of the surface is available. The measurements were made on July 12, 1962 after the well field had been idle about 14 hours. The average elevation of the water level in two wells tapping the water-table aquifer was 7.6 feet above sea level; the average elevation in six wells tapping the first artesian aquifer was 8.1 feet above sea level; and the average elevation in three wells tapping the second artesian aquifer was 9.6 feet above sea level. The nonpumping piezometric surfaces of both the first and second artesian aquifers at the Venice well field doubtless lie above the water table most, if not all the time.