Florida Geolcgical Sirvey


Icr any anomalous lemperature decreases. Temperatures generally ranged between 80 and 112 degrees F al depths greater than 1.000 feel and generally increased with deplh; therefore. no cyclic or convective circulation is suspected in the study area. Temperature decreases have Oeen documented in south Florida where the Strails of Florida are adjacent lo the Florida Platform, The occurrence of convective ckrcula. lion should be investigated when injection wells are proposed for Ihese areas.

 GROUND-WATER CHEMISTRY ANALYSIS

 Introduction

 Water-quality data, confining zone, and injeclion zone information for seven wells in Brevard County and one well in Indian River County {Hercutes Corporation) were analyzed for this investigation. Three wells, the Merritt Island, Soulh Beaches, and D. B. Lee injection wells, were chosen for detailed study because ol obvious trends observed in water-quality data. For ihese wells, confining, injection, and monitor zone hithologies were examined lo determne any physical properties that might help explain observed monilor zone contamination. Determining the mechanical i.nlegrity of the injeclion wells was beyond the scope of this study.

 The injection inlervats of all eight wells occur in the Boulder Zone of the lower Floridan aquifer system (Figure -36), in the Oidsmar Formalion (with ihe possible exception of Me Port Malabar injection interval where the Boulder Zone is riot well developed; see Plate 3). This zone is generally highly fractured and cavernous, with transmissivily values ranging up to 21 Million gpd.tt (Haberfeld. 1991). The high transmissivities in the injection zone, and pumping rates which can be tens-of-millions of gallons per day, result in only minimal increases in wellhead pressure in most weEs (Haberfeld, 1991 ), This implies the possibility that ihe injected waters are circulaling freely. Fractures, discontinuities, and cavities in


the designated confining zones of 'he wellsc could provide ,orduits !or thle cirou~a! ng water.

 The inlected fLuids are generally low-salinily, treated municipal waste waler. Industrial waste waters are inlected at 1he Harris Corp. and Hercules, Inc. sites. Injecled waters are lps dense than formalion water, and siice fluids in the injecton and lower monitor zones are high:y saline. "contaminatdon" irorT irjecled ill.ids will be seen as Iresheoing trends in mon'lor well data. For example, such trends show up as a decrease in total dissolved solids (TDS) and.cr chloride concentration, Occasionally. marKed increases in these paramelers are observed, and this is attribuled to deeper saline waters being displaced upward by injected fluids (J. Haberfeld, DES, personal communication, 1991).

 Nitrogen conleni is monilored tocaJse treated waste water will generally have higrier nit.,ogen concentrations than ambient formation water. It is measured as tolal kjeldahl nitrcgen .'TKNI', which is organic nitrogen plus ammonia. Another important measuremnt is the depth al which ihe TDS value exceeds 10,000 mgiL. Uriled Slates Environmental Protection Agency guidelines slate that the TDS value of formalion walers In an injection zone musl exceed 10.0W0 rn.-.L, so consultants note Ihe depth al whch the transilion occurs. For 1he transition deplis, only prein section values are availab'e.

 The TDS, chloride, and TKN are among the pararrieters lracked in the varici. monilor zones, and these three were chosen fc.r close nvestigalion because time series data on them are available for the morilor zones of the injeclion wells.

 The three primary wells are the Merrilt Island, the South Beaches, and mhe D_ B, Lee irje-clion wells. These are discussed first, and are followed by summaries of dala ior the Harris Corp., Grant Streel, Porl Malabar, West Melbourne. and Hercules, Inc. injeclion wells.