Bulletin No. 64


 Hydraulic head results are summarized in Figures 29, 30 and 31 for the Harris, Port Malabar and D. B. Lee wells. The water level readings observed during daily low tides were analyzed for the D. B. Lee wells (Figure 31) in an attempt to partially filter the effects of diurnal tidal loading (Figure 28) on the confined aquifer systems. Similar patterns of hydraulic head fluctuation within both the Port Malabar and D. B. Lee monitor wells may be indicative of a hydraulic connection between the injection and monitor zones (Figures 30 and 31) at these two sites.

 The D. B. Lee 1,500 and 1,800-foot monitor wells (Figure 31) demonstrate patterns of hydraulic head fluctuations that are suspiciously similar. Both wells are located in a highly fractured or vuggy dolostone (Plate 3) and there may be a hydraulic connection between the two. Although not as apparent, the shallow monitor well, located in the middle confining unit, is also exhibiting a pattern of water level fluctuation similar to the two deeper monitor wells. These similar responses could be due to a hydraulic connection between the wells, or they may be reacting to external loading stresses such as barometric pressure (Figure 28). Hydro Designs (1989) conducted four injection/recovery tests on the D. B. Lee injection and monitor well system. The results (Figures 32 34) of the first test are presented in this report.

 The wells were allowed to stabilize (Figure 32) prior to the first test in order to quantify and remove oceanic tidal loading effects on pressure fluctuations in the monitor wells. The injection/recovery tests were designed so they would not interfere with the normal operation of the plant. Theoretically, the recovery phase should be the mirror image of the injection phase. This, however, was not the case (Figure 34) because the injection flow was automatically reduced in steps by the injection pumps in operation (Hydro Design, 1989).


 A nearly simultaneous increase of hydraulic head in the injection and monitor wells during the injection tests (Figure 33) strongly indicates a hydraulic connection between the injection and monitor zones. A definite trend in the change of water chemistry in each of the monitor wells (see Ground-Water Chemistry Analysis this report) supports this conclusion. The exact cause of the upward leakage cannot be determined. Lack of structural integrity of the well bores is one possibility. The D. B. Lee injection and monitor well system is located in a highly fractured or vuggy dolostone (Plate 3). A lack of confinement between injection and monitor zones would occur if the fracture network is connected. It is also feasible that both lack of confinement and improper well construction could be contributing to upward leakage from the injection zone.

 Geothermal Gradients

 Deep well temperature surveys in southern Florida have shown that geothermal gradients underlying the Florida Platform are affected by the presence of cold sea water. At depths of 1,500 to 3,000 feet the water in the Floridan aquifer system becomes anomalously cooler with depth (Meyer, 1989). The average temperature near the cold sea water bodies averages about 60 degrees F and increases to 108 degrees F along the central axis of the Florida Plateau (Kohout et al., 1977). Horizontal and vertical temperature distributions suggest that cold, dense sea water flows inland through cavernous dolostones of the Boulder Zone where it becomes progressively warmed by geothermal heat flow. The reduction of density produces upward circulation. After mixing with less saline water in the upper part of the aquifer, the diluted saltwater flows seaward to discharge by upward leakage through confining beds or through submarine springs on the continental shelf (Kohout et al., 1977) (Figure 35).

 Borehole temperature logs, provided by the various consulting fIrms were closely inspected