Florida Geological Survey


for the chloride plot is 0.92. The TDS value is
0.54, but jumps to 0.74 when the obvious outly-
ing values are removed. For the TKN regres-
sion, values from February 1987 to April 1988
were used, to determine the significance of the
increase in concentration. The R-squared value
for that period is 0.71. These high R-squared
values tend to support the interpretation that
possibly fractures and the general discontinuous
nature of the confining interval have allowed
injected fluids to migrate vertically through the
confining layer,

 South Beaches

 The South Beaches injection well has a total
depth of 2,916 feet BLS in the Oldsmar
Formation. There are two separate monitor
wells at the site. The upper Floridan aquifer sys-
tem well monitors the zone from 300 to 350 feet
BLS in the Ocala Limestone, and the lower
Floridan aquifer system well monitors Irom
1,550 to 1,700 feet BLS in the Avon Park
Formation (Appendix A2). The confining zone,
as defined by Dames and Moore (1985),
extends from 1,665 to 2,081 feet BLS in the
Avon Park and Oldsmar Formations. The injec-
tion zone extends from 2,081 to total depth, but
the interval with the most fractures and cavities
is from 2,081 to 2,760 feet BLS (Dames and
Moore, 1985).

 The lower monitor zone, in the lower Avon
 Park Formation, has interbedded dolostone,
mudstone, and wackestone, with porosities
ranging from 10 percent to 15 percent, moder-
ate to good induration, and apparently low per-
meability,

 The confining zone, in the lower Avon Park
 and upper Oldsmar, has interbedded mudstone,
 wackestone, packstone, and dolostone layers.
 Porosities range from five percent in a few
 interbedded cherty layers, to 20 percent in the
 wackestones and packstones. Bolh induration
 and permeability have wide ranges, from low to
 high in alternating layers. Siickensides related to


fracturing andlor faulting were observed in cores
within and above the confining zone.

 The background water-quality report (Dames
and Moore, 1985) on the lower monitor zone
shows that before injection the average TDS
value was 23,975 mg/L, and the average chlo-
ride value was 14,410 mg/L. In this area TDS
values exceed 10,000 mg/L at approximately
1,250 leet BLS. No TKN measurements were
taken, but nitrogen, measured as nitrate, was
0.03 mg/L.

 Dramatic changes in these values have been
observed since injection began in May 1987.
TDS fell from over 21,000 mg/L to less than
10,000 mg/L (Figure 40). Chloride values tell
from over 16.000 mg/L to less than 5,000 mg/L,
starting in July 1987 (Figure 41). These changes
are attributed to injection waters rising through
the confining units. Values of TKN show a pat-
tern similar to that of the Merritt Island well lower
monitor zone. There was a rise Irom approxi-
mately 0.5 mg/L to a peak at about 3.0 mg/L,
and then a decline (Figure 42). This is again
attributed to the increasing efficiency of the
treatment plant at the South Beaches site. It is
not known why the values increased rapidly in
mid-1991. No trends were observed in the upper
monitor zone.

 Regression results show an R-squared value
of 0.78 lor the observed chloride trend, with the
value increasing to 0.87 when outliers are
removed from the calculations. The R-squared
value for the TDS plot is 0.9. Regression of TKN
values was done for the period Irom Juty 1987
to March 1988, to determine if the increasing
concentration trend was significant. The R-
squared value for that period is 0.88. These val-
ues tend to support the conclusion that the Irac-
tures, cavities, and the discontinuous nature of
the confining zone have allowed migration of
injected fluids into the monitor zone.