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The study area is located along the eastern boundary of Everglades National Park (Fig. 1). Karst limestone underlies the peat and marl throughout much of the Everglades (Fish and Stewart 1991); it consists of the Miami Limestone and the Fort Thomson Formation (Fig. 2) (Causaras 1987, Perkins 1977), which combined form the Biscayne aquifer in the upper part of the surficial aquifer (Fig. 2). The Fort Thompson Formation is 3-17 m deep, and it thickens slightly to the east, where it underlies the Miami Limestone (Fish and Stewart 1991). The marine limestone of the Fort Thompson Formation generally is riddled with solution cavities, that are usually 6 cm or less in diameter, but are so abundant that much of the limestone resembles a sponge. As a consequence, this formation is highly permeable (Fish and Stewart 1991). The Miami Limestone crops out along the eastern margin of ENP and is locally known as "the Rocky Glades" (Fig. 1). It general, it appears the Miami Limestone does not have a network of open cavities as well developed as the Fort Thompson Formation, and in many areas the cavities are at least partly clogged with lime mud and sand, reducing the average hydraulic conductivity to much less than the underlying limestone of the Fort Thompson Formation (Fish and Stewart 1991).

Figure 1. Map of Everglades National Park, Florida, with relevant features of the Park, main water control structures, and location of the 15 wells used in this study. [larger image]

The Atlantic Coastal Ridge ranges from 1.5 to 6 m above sea level in the study area and bounds the Everglades marshes on the east. The ridge is about 5 to 8 km wide throughout most of its length, widening to nearly 16 km at its southernmost terminus. The ridge is a natural barrier to eastward-flowing drainage, except in its southern part, where it is breached by low-elevation sloughs oriented perpendicular to the trend of the ridge. Before development, the Everglades were typically submerged by surface water most years, drainage was slow, and surface water flow was directed to the south and southwest by the Atlantic Coastal Ridge.

The Miami Limestone and Fort Thompson Formation of south Florida consists of five unconformity-bounded, time-stratigraphic marine units (Fig. 2) termed, from oldest to youngest, Q1 through Q5 (Q for Quaternary) (Perkins 1977). We defined a Q unit as high-frequency cycle (HFC), i.e., the smallest set of genetically related lithofacies deposited during a single relative rise and fall of sea level: the lower and upper bounding surfaces of the HFC are at the turn-around from a relative sea-level rise and a relative sea-level fall (Kerans and Tinker 1997, Lucia 1999). The "Q units" of Perkins (1977) and the HFCs of this study correspond, except Q3 is divided into Q3B (upper HFC), and Q3A (lower HFC). Several investigations presented evidence for at least one hydrostratigraphic unit of very limited ground water flow within the Biscayne Aquifer (Cunningham and Wright 1998, Genereux and Guardiario 1998, Guardiario 1996, Kaufman and Switanek 1998, Nemeth et al. 2000, Sonenshein 2001), at the top of the Q3B in the Fort Thompson Formation (Genereux and Guardiario 1998).

Figure 2. Cross-sections showing sample locations at test coreholes. See Fig. 1c for location of cross-sections. On the right side of each transect are represented the lithostratigraphic units (Causaras 1987), the "Q units" (Perkins 1977), and the high-frequency cycles (HFC). [larger image]

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