Florida Geological Survey


and ranged belween 85 lo 190 feet (Plate 3). The cavernous nature of the Boulder Zone in peninsular Florida diminishes northward (Miller, 1986) (Figure 24).

 The carbonates immediately overlying the Boulder Zone consist of inlerbedded wackestones, packslones and doloslones of the upper Oldsmar Formation (Plates 1 and 3). Porosities, estimated from the sonic logs, are generally greater than 20 percent. Geophysical logs, samples and borehole videos suggest thai this zone is fractured in some injection well boreholes (Plale 3).

 Where the Boulder Zone is utilized for waste disposal. there is a traditional view that the dense doloslone immedialely above and below the Boulder Zone contains no secondary porosity and operates as a confining layer. However, a sludy ol four injection sites along the east coast of Florida by Safko and Hickey (1992) concluded that fracture porosity is the principal type of secondary porosity both within the Boulder Zone and the dolomlic rocks that lie above it. The present study utilizing core samples, borehole videos and geophysical logs, supports this hypothesis.

 Confining Layers

 Possible conlining layers above the Boulder Zone, within the lower Floridan aquifer system, were defined conservatively in this study and are not always in agreement with confining layers delineated by Ihe various consulting firms (Plate 3 and Appendix A). Criteria used for defining layers of confinement are based on geophysical logs and lithologic samples, In general, non-vuggy, fractureless micritic limestone and or microcrystalline dolostone with sonic log porosilies less than 20 percent, that are traceable and correlative in the subsurface belween the injection wells, are defined as confining layers.


 There is a well defined, highly correlative and widespread glauconitic, micritic wackeslone located in the uppermost Oldsmar Formation (Plates 1 and 3). The glauconite marker bed is located approximately 60 to 235 feet above Ihe Boulder Zone (Plate 3), Porosities estimated from sonic logs range between 10 to 37 percenl and fracturing and/or vuggy lithology is absentThis layer is between 35 to 45 feet thick and appears to be a well defined zone o1 confinement (Plates I and 3). Hydraulic conductivity analyses conducted by the various consulting firms (Appendix A) for the Merritt Island, West Melbourne and Port Malabar injection wells report values ranging between 10-5 to 10'6 cts supporting the assumption that this layer is confining.

 Locally, above the glauconite marker bad, there is P zone of rocks with confining qualities (Plate 3). This zone is located in the lower Avon Park Formation and has been delineated as the lower Avon Park confining zone by 1he Florida Geological Survey (Plate 3).

 Geophysical logs, borehole videos and tithologic samples suggest that he lower Avon Park confining zone contains fractures ancor vuggy lithology. The data are insufficienl to determine the degree of fracture connectivity within these layers and it is not known whether these layers can transmit water via the fraclure network, Thus, it is not known if I he lower Avon Park confining zone is a good confining layer,

 The rocks underlying the Boulder Zone are dense micro-crystalline doloslones wilh porosities less than 15 percent, These dolostones are fraclured in places and extend below the total depth of the injection wells. These carbonates appear to be a layer o1 confinement (Plale 3).

 Fractures and Vertical Flow

 As slated previously, analysis of geophysical logs, lithologic samples and borehole videos indicate that numerous fractures exist through-