Hydrogeology and Groundwater Quality of Highlands ... - USGS

52 Hydrogeology and Groundwater Quality of Highlands County, Florida
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100
20
Magnesium
40
and chloride concentrations in water from the intermediate
aquifer system are shown in figures 41 and 42. Specific
conductance values for Highlands County ranged from 66 to
11,500 µS/cm, with a median value of 424 µS/cm. Chloride
concentrations in water ranged from 3.8 to 3,770 mg/L, with a
median value of 13 mg/L. Specific conductance and chloride
concentrations were lowest primarily in the northwestern and
south-central parts of the county and highest in the southwestern
and southeastern parts. Sulfate concentrations ranged
from 0.12 to 111 mg/L, and hardness as CaCO3 (calcium
carbonate) concentrations ranged from 17 to 1,200 mg/L.
The median values for sulfate and hardness were 2.5 and
175 mg/L, respectively. Nitrate, orthophosphate, and phosphorus
concentrations ranged, respectively, from 0.004 to less
than 0.04 mg/L, 0.004 to 1.5 mg/L, and 0.003 to 1.6 mg/L.
The highest values for specific conductance, chloride
concentration, and water hardness (as CaCO3) in the intermediate
aquifer system were obtained from a 500-ft deep
well (well 22) in southern Highlands County. These values
also were the highest values reported from any aquifer in the
county. The specific conductance of water from this well was
80
60
PERCENT
80
100 0
60
40
Calcium
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20
0
Sulfate plus Chloride
20
20
40
60
20
40
Sodium plus Potassium
40
60
60
80
100
0
80
80
100
100
100
100
80
80
PERCENT
100
0
Calcium plus Magnesium
60
60
80
40
40
60
20
20
20
40
Carbonate plus Bicarbonate
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40
60
11,500 µS/cm. Hardness and chloride concentrations were
1,200 and 3,770 mg/L, respectively. Sulfate concentration,
although not anomalously high, was 111 mg/L. The source of
this highly mineralized water is probably relict seawater that
entered the intermediate aquifer system during Pleistocene
age. This zone of mineralized water, probably trapped in strata
of low permeability, has not been removed by the modern-day
freshwater flow system.
Upper Floridan Aquifer
0
20
0
100
PERCENT
80
80
The Upper Floridan aquifer is the most productive and
widely used aquifer in Highlands County. In much of the
county, water in the Upper Floridan aquifer generally meets
FDEP primary and secondary drinking-water standards.
However, more mineralized water is present at depth beneath
the entire county. Chemical analyses of groundwater samples
from wells completed in the Upper Floridan aquifer indicate
differences in the ionic composition of water, and several
chemical types of groundwater occur in the study area.
60
Sulfate
40
20
100
Chloride, Fluoride, Nitrate plus Nitrite
Figure 40. Chemical composition of water from the intermediate aquifer system.
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