The Surficial aquifer is a principal source of fresh drinking water in south Florida. Sediments within the aquifer were deposited during the middle Pleistocene epoch and range in age from 1.8 million years before present (BP) to 13,000 years BP (Perkins, 1977). These Surficial aquifer sediments are composed mainly of shallow water marine facies, including coral limestones, beach and offshore sandbar complexes, lagoonal limestones, and an oolitic ridge along the coast of Miami (Perkins, 1977; Hoffmeister, 1974). The Surficial aquifer includes the highly transmissive Biscayne aquifer, which underlies Miami-Dade, Broward and eastern Palm Beach Counties. The Biscayne aquifer is thickest beneath the Atlantic coastal ridge to the east of the Everglades, and it thins from east to west, disappearing beneath the north-central Everglades. Aquifers to the west of the Biscayne and beneath the Everglades generally have been ignored as potential sources of ground water, both because of the lower transmissivities (Fish, 1988) and because of the higher total dissolved solids in ground water beneath the Everglades (Howie, 1987; Miller, 1988).

Except for a few studies mentioned above, there is little comprehensive information available about the hydrogeology beneath the north-central Everglades. Previous site-specific investigations included various studies at ENR. A study by Hutcheon Engineers at ENR was associated closely with engineering design projects for STAs, but provided relatively little in the way of lithologic or hydrogeologic data. Rohrer (1999) broadly characterized the hydrogeology of the ENR from boreholes placed on ENR levees and focused attention on the near-surface layer of the Surficial aquifer. A goal of the present investigation was to characterize in detail the geology and hydraulic properties of the Surficial aquifer at new drilling sites in ENR and WCA-2A. Of particular importance was identifying layers of relatively high or low hydraulic conductivity and their relation to physical properties and geologic classification of aquifer layers.