ABSTRACT


 A common problem for coastal communities in Brevard County has been the disposal of liquid waste products. A favored solution utilizes injection-disposal wells whereby liquid waste is pumped underground into highly permeable rocks within the non-potable portion of the lower Floridan aquifer system. Ground-water chemistry data from monitor wells at several Brevard County injection sites suggest that the presence and/or lateral continuity of suitable confining rock above the injection zone is questionable and indicate that a better understanding of the lower Floridan aquifer system is needed. Thus, the purpose of this study is to detail the geologic framework of the lower Floridan aquifer system in Brevard County.

 Strata of the lower Floridan aquifer system in Brevard County dip generally to the southeast with an average dip angle of 0.1 degree. Several lines of evidence suggest the possibility of faulting in Brevard County. The inferred faults strike north-south and are downthrown to the west.

 Cores of lower Floridan aquifer system strata commonly exhibited some degree of fracturing. In general, fractures appear to be restricted to well indurated or highly cemented carbonates, principally dolostone. Slickensided surfaces, lacking well defined fracture planes, were observed in moderately to poorly indurated limestones.

 Strata of the lower Floridan aquifer system in Brevard County are characterized by Paleocene to Middle Eocene, interbedded limestones and dolostones. Limestones are generally fossiliferous, moderately to poorly indurated, and have high primary porosity. Dolostones are typically well indurated and have fossil moldic and vugular porosity.

 In Brevard County, the Floridan aquifer system generally consists of two major permeable zones separated by a middle confining unit of lower permeability. The middle confining unit in the study area consists of dense dolostone with interbedded limestones which act as a single leaky confining unit within the main body of the permeable carbonates of the Floridan aquifer system. Carbonates below the middle confining unit in the lower Floridan aquifer system are predominantly low permeability, interbedded dolostones and limestones with zones of moderate to high permeability.

 The "Boulder Zone," a subzone of the lower Floridan aquifer system, is the primary injection horizon in Brevard County and consists of highly fractured and cavernous dolostones which exhibit high transmissivities. Above the Boulder Zone, there are layers of carbonates that have confining qualities. Evaluation of geophysical logs, lithologic samples and borehole videos from Brevard County injection wells indicate that numerous fractures exist throughout the lower Floridan aquifer system.

 Analysis of monitor zone ground-water chemistry data showed that the majority of the wells in the study exhibit trends in water quality to some degree. These trends, barring wellbore mechanical problems, are attributed to the upward migration of injected waste waters along permeable conduits related to fractures, dissolution cavities, and vertical and lateral lithofacies variations. The middle confining unit of the Floridan aquifer system in Brevard County is probably best described as having a leaky confining character.