Bulletin No. 64


out the lower Floridan aquifer system (Plate 3). When determining confining properties, the presence or absence of fracture syslems is extremely important- Fracture systems, with the proper orientation and connectivity, can transport water through rocks that appear to be confining.

 Given the right geologic setting, brittle rocks od low porosity are most susceptible to fracturing (Dornenico and Schwartz, 1990). Dolostone is considered one of the most fracture-prone sedimentary rocks, second only to quartzile (Stearns, 1967) (Figure 25). Van GolI-Racht (1982) cites three cases where stress relaled Iractures may occur1. In response to folding and/or laulting;
 2. Deep erosion or removal of the overburden,
 which will produce differenlial stresses that
 can cause fractures;
 3. Rock volume shrinkage (shrinkage cracks)
 where water is lost, for example, in shales
 or shaley sands:

 Cases 1 and 2 are believed to have occurred in 1he study area (see Lithosiratigraphy and Structural sections for further discussion) and furlher support Safko and Hickey's (1992) hypothesis ol vertical Iracturing of doloslones ovedying the Boulder Zone.

 Increases in hydraulic conductivity due to secondary porosity can occur as a result of dissolulion of limestone by circulating ground water moving along fractures and bedding planesAnalyses of the sediment cores, geophysical logs and borehole videos indicate fractured dolostones in and above the injection zone (boulder zone) in the D. B. Lee and other injection wells (Plate 3). Normal faulling in the area where the West Melbourne and D_ B. Lee wells are located could result in increased secondary porosity along the fault plane and enhanced fracturing locally (see Structural Geology section for further discussion).


 Hydrogeologically, the most important fracture properlies are orientation, density, aperture opening, smoothness of fracture walls, and most importantly, the degree of connectivity (Domenico and Schwartz, 1990). If a given set of fractures does not exiend through a confining layer or are not interconnected, then the rock cannot transmit water via the fracture network. As previously stated, there is strong evidence for fractures throughout the rocks within the lower Floridan aquifer system. The degree of connectivity belween these fractures is nol known and the water transmiting character is uncertain.

 Dissolutional enlargement ol fault planes and fractures within zones of relatively impermeable carbonates can dramalically increase vertical and lateral hydraulic conductivity and result in localized transport of different waters through potential confining layers. Fault planes can lunction as conduits causing water to breach contining layers and bypass monitor wells. Figure 26 is a schematic diagram demonstrating these phenomena.

 Hydraulic Head in Wells

 By definition, a true impervious layer will not transmit pressure, due to a hydraulic head increase, between confined aquifers. Hydrogeologic units that are separated haom each other by a confining layer(s) should demonstrate conlrasting hydrologic behavior. Dislinci hydrologic systems which respond similarly suggest a hydraulic connection. Differences in head values and fluctuation between the mnilcr and injeclion wells indicate hydraulic separation. When the hydraulic heads fluctuate in a similar pattern a hydraulic connection could be present and vertical flow may be occurring.

 However, confined aquifers are compressible and elastic over certain stress ranges and thus respond to changes in forces acting upon them. These stresses include periodic loading by ocean and earth tides, earthquakes; fluctuations