Because of cavities and shell 

 beds, the Fort Thompson Formation and 

 Ochopee Limestone are extremely per- 

 meable and transmit water readily. 

 Pumping tests conducted by the SFWMD 

 on Well 2012 (220 feet or 67.1 meters 

 deep) show that the transmissivity 

 of the aquifer is 220,000 gallons 

 per day per foot (2,732 m /day). Flow 

 meter logging of this well revealed 

 that about 95 percent of the water 

 produced by the well is produced in 

 the interval between the bottom of 

 the casing at 12 feet (3.7 meters) 

 and a depth of 60 feet (18.3 meters). 



AREAL WATER QUALITY RELATIONSHIPS 



During the studies conducted by 

 AES and Geraghty & Miller, water sam- 

 ples were collected from the network 

 of observation wells in 1978 and 

 1980. Analyses were performed for 

 chlorides, specific conductance, and 

 a number of other parameters. Be- 

 cause sodium chloride is a predomin- 

 ant constituent of sea water, the 

 relationship between saline and fresh 

 ground water in the area was deter- 

 mined by studying the distribution 

 of the chloride ion (expressed as 

 mg/1 of CI ). Samples were analyzed 

 from wells less than 10 feet (3 me- 

 ters) deep, from wells tapping the 

 principal water-bearing zone, and 

 from the lake. The results, plotted 

 on Figure 3, show the distribution 

 of saline water in the area. 



With the exception of the sam- 

 ple from Well 7, water from wells 

 tapping the principal water-bearing 

 zone and the deep portion of the 

 lake contained chlorides well in ex- 

 cess of the normal concentration of 

 sea water (18,000 to 19,000 mg/1): 

 chlorides in Wells 1, 2, 3, and 5 

 ranged between 22,000 and 25,000 

 mg/1. Water from wells tapping the 

 principal zone north of the Belle 



Meade Grade is salty to brackish 

 ranging from 10,100 gm/1 of CI in 

 Well 6 to 225 mg/1 in Well 8. Pro- 

 ceeding northeast from the Belle 

 Meade Grade, the chloride concentra- 

 tion of the ground water lessens. 

 North of the grade, water from the 

 shallow wells is fresh, less than 

 200 mg/1, with the exception of 

 Well 6, where chlorides of 988 mg/1 

 were found. South of the grade, 

 water from the shallow wells ranges 

 from 616 to 23,100 mg/1, while the 

 shallow portions of the lake had 

 chlorides of 3,661 mg/1. 



The chloride concentration of 

 the ground water north of the Belle 

 Meade grade represent a normal dis- 

 tribution found in shallow aquifers 

 in the coastal areas. Proceeding 

 inland from the grade, the chloride 

 concentration in the principal 

 water-bearing zone diminishes; at 

 Wells 8 and 10 the water in both 

 zones is fresh for all practical 

 purposes . 



South of the grade, a different 

 situation exists. The distribution 

 of chlorides represents a combination 

 of a unique natural condition and the 

 results of man's activities. The 

 hypersaline ground water present in 

 both the shallow and the principal 

 zones and in the lake is a natural 

 condition. Normally shallow saline 

 ground water in the coastal areas has 

 the same composition as sea water. 

 The observed chloride levels in ex- 

 cess of 18,000 to 19,000 mg/1, the 

 concentrations found in sea water, 

 require the presence of some mechan- 

 ism of concentration. It is believed 

 that the concentrating mechanism is 

 one of or a combination of the fol- 

 lowing natural processes. The first 

 possibility is evaporation. During 

 periods of abnormally high tides, 

 such as those accompanying hurri- 

 canes, the area will be inundated. 

 When the tide recedes, pools of sea 



256 



