Abstract Introduction Study Area Aquifer Framework and Definitions Transmissivity, Hydraulic Conductivity and Storage Coefficient Hydrogeology - Sediment Hydraulic Conductivity   -  W. Broward Co.   -  Central and E. Broward Co. > Aquifer Delineation - Transmissivity Distribution Ground-Water Flow System Summary References Cited PDF Version

Contour maps were prepared that delineate the surficial aquifer system and the aquifers within the system. These maps are based on the aquifer definitions previously given, aquifer test results, and the hydrogeologic sections (figs. 15-22).

A contour map showing the altitude of the base of the surficial aquifer system below sea level is given in figure 35. In addition to the test holes drilled in this study, eight others from Parker and others (1955) or from U.S. Geological Survey files were used to select the base. The base of the surficial aquifer system is at a relatively uniform altitude of 150 to 200 feet below sea level (about 160 to 210 feet below land surface) over the western two-thirds of the county. The base slopes gradually downward to the east and also into a small depression at the North Everglades east site (G-2315, fig. 3 and fig. 15). The base rises to a high area shown as a north-south ridge through the Cypress Creek Canal west site (g-22341, fig. 3 and fig. 16) where more than 60 feet of sandy silt was found below the base of the aquifer system. This trend could continue southward, passing near the Markham Park site (g-2321), to the Snake Creek Canal west site (G-2317) at the Dade County line. However, the latter test hole was not drilled sufficiently deep to be certain that the base had been reached. A continuation of the ridge-like high area of the base has been recently found to the north on Palm Beach County (W.L. Miller, U.S. Geological Survey, oral commun., 1984). Eastward from this trend, the base slopes downward at 10 to 20 ft/mi to altitudes of 300 to 400 feet below sea level along coastal Broward County.

Contours on the base and the top of the highly permeable gray limestone aquifer in the Tamiami Formation are shown in figure 36. The aquifer, as mapped, includes all intervals of the gray limestone that are at least 10 feet thick and have an estimated hydraulic conductivity of at least 100 ft/d. Also included is the coarse shell sand at the Twenty-Six Mile Bend site, although it is not known for certain that it connects with highly permeable gray limestone beds. The configuration of the top is complex. It generally slopes downward to the east from 20 to 85 feet below sea level along the Collier County line to about 110 feet below sea level near the eastern edge of west Broward County. In contrast, the base is more uniform in altitude. Its configuration is slightly basin shaped, the deepest point being 173 feet below sea level along Alligator Alley is about 90 feet thick. The north Everglades west site (G-2314, fig. 15 and fig. 19) has the greatest thickness, about 110 feet, but the average permeability at the site is much lower than along Alligator Alley.

Figure 35. Generalized configuration of the base of the surficial aquifer system in Broward County. [larger image]

The eastern edge of the gray limestone aquifer is near the boundary between west and central Broward County, except near the Palm Beach county line. The eastern edge is mapped at the rapid transition from highly permeable limestone or contiguous shell sand (hydraulic conductivity of at least 100 ft/d) to much less permeable facies, except near the Hillsboro Canal west site (PB-1428, fig. 15). East of the site, the gray limestone may change to low permeability fine-grained facies of the Tamiami Formation, as in most of central Broward County, or it may connect directly with the Biscayne aquifer. Recent test drilling has shown that the aquifer continues into southwest Palm Beach County (W.L. Miller, U.S. Geological Survey, oral commun., 1984) and into northwest Dade County. Figure 36 indicates that it also extends into Collier County and Hendry County.

The base and approximate western and northern limit of the Biscayne aquifer are shown in figure 37. The limit is drawn where the thickness of very highly permeable limestone or calcareous sandstone is estimated to decrease to less than 10 feet. It follows relatively close to the boundary given in figure 8 by Klein and others (1975), except that the northern half of north-central Broward County was excluded because test drilling conducted in this investigation did not indicate sufficient thickness of very highly permeable limestone in the area. The sediments in the excluded area are predominantly muddy sands and shell or limestone that are generally not highly permeable. The base is drawn on the bottom of highly permeable limestone or sandstone in the Tamiami Formation that is virtually contiguous with overlying rocks of very high permeability in the Fort Thompson Formation, Anastasia Formation, or Tamiami Formation. In General, the Biscayne aquifer is shallow, and the base deepens gradually in west and central Broward County. However, the aquifer thickens, and the base deepens very rapidly in the coastal area to more than 300 feet below sea level.

A significant difference between figure 37 and previous maps is that the very thick, highly permeable, calcareous sandstone and limestone beds at depth in the coastal area are included in the Biscayne aquifer. In agreement with this interpretation, Tarver (1964, p. 8) suggested that the base of the Biscayne aquifer is about 400 feet below sea level near the coast in northeast Broward County. Previous test data near the coast were sparse because salt water intrusion is a problem. Other contour maps (such as shown in figure 8) or reports typically indicate a depth of about 160 feet based on wells drilled primarily to zones used for municipal supplies.

Figure 36. (above) Generalized configuration of the top, base and approximate eastern limit of the gray limestone aquifer in Broward County. [larger image]

Figure 37. (above) Generalized configuration of the base and approximate western and northern limit of the Biscayne aquifer in Broward County. [larger image]