Bullelin. No 64


ernous and fractured nature of the doioslone commonly causes boulder size pieces of dole. stone to be dislodged during the drillirng process giving rise to Ihe lerm -Boulder Zone" by drillers and subsequenlly adopled by Kohout (1965) and later aulhors- In areas where the salinity of 1he waters in the Boulder Zone is greater than 10,000 mg/L, the Boulder Zone is used as a receiving zone for underground injection of industrial wastes and treated effluent. A more detailed discussion of the hydrogeology ol the middle confining unit, lower Floridan aquifer system and Boulder Zone is presented in subsequent sections of this repod.

 Numerous Tertiary regressive/transgressve sequences have pro-duced a diverse carbonate lithology in the Floridan aquifer system (Plate 1). A typical sequence of deposition would vary from low energy, open platform, micnlic sediments grading into progressively higher energy packstones or grainstones cnaracterislic of a shoaling environment to low energy, tidal Ilat, fine-grained sediments. As a result of these numerous sea level Ituclualions and subsequent diagenelic changes, locally variable, complex hydrogeologic conditions exist throughout the Floridan aquiler system.

 The Floridan aquiler system does nol necessarily conform 1o eilher lJithostraligraphic or chronostrallgraphic boundaries and lherefore, the top of the Floridan aquifer system (Figure 10) coincides with the uppermost vertically-continuous, permeable, Eocene ro Lower Miocene carbonate beds (SEGS, 1 986). In the study area, the top of the Floridan aquifer system is contiguous with the lop of the Eocene Ocala Limestone (Figure 10) and occurs at elevations ranging from .100 to deeper than -350 feet NGVD (Figure 13). The thickness of 1he Floridan aquifer system in the study area ranges between 2,300 lo more than 2,900 feet and generally increases to the soulh (Figure 14) (Scolt et al., 1991),


 Recharge lo ihe Floridan aquifer system is directly associated with the degree of hydraulic confinement of the system. The highest rales of recharge occurs in northern Brevard County where ihe Floridan aquiler syslem is unconfined or poorly confined (Figure 15). Sinholes 1hat breach the niermediate confining unil and provide hydraulic communication between the surficial aquifer system and ihe Floridan aquifer system can result in either recharge to or discharge trom the Floridan aquifer system. In 1he study area recharge will occur in northern Greard County and western Indian River County (Figure 15). Discharge to the surlicial aquifer system will occur in areas of artesian flow (Figure 16)The potenliometric surface and regional hori2gntal flow of the Floridan aquifer syslem are also related to tne degree of conlinement. The potentiometric surface ol the upper Floridan aquifer system in the study area ranges from approximately 5 to 40 feet {Figure 17) and lateral flow is generally soulh. Where tMe potentrometric surface is higher than ihe surface elevation, artesian Ilow will occur (Figure 16), Arlesian conditions are present over most of the study area- In areas where there is relatively poor or non-existeni conlinerment, and where land surface is nigher than 1he potenliometric surface, (i.e., weslern Indian River County) arte. sian conditions are absent (Figure 16) and recharge to 1he Floridan aquifer system may occur (Figure 15). Transmissivity of the upper Floridan aquifer system (Figure 18) is generally higher in the southern portion of the study area but is locally variable because of complex hydrogeologic heterogeneily.

 Massively bedded anhydrite usually occurs in the lower two-thirds of Paleocene rocks (Miller, 1986). The lop of the sub-Floridan conlining unit (Figure 19) is defined in terms of a permeability contrast that limils the depth of active groundwater circulation and does not represent any particular stratigraphic or lime uni (Figure 10). The pnjecilion and monitor wells in the study area are not deep enough 1o encounter the subFloridan confIning unit.