REPORT OF INVESTIGATIONS No. 41                   13

1090 ppm chloride. Both of these are adjacent to saline surface-water bodies. Wells penetrating the -underlying Floridan aquifer, at and near these locations, produce water low in chloride. The saline water is presumed, therefore, to have leaked from the bays through the water-table aquifer.
    Apparently, the aquiclude overlying the Floridan aquifer (fig. 3). in the coastal and bay area is sufficiently impermeable to prevent leakage of water from the overlying aquifers. The occurrence of chloride in water in the Floridan aquifer does not appear to be related to areas of high chlori 'de in water in the overlying sediments or to the bays. Water levels in the Floridan aquifer have been lowered below water levels in both the water-table aquifer and the secondary artesian aquifer, by pumping in the major well fields. Extended periods of low water levels in the Floridan aquifer have not resulted in an increase in the chloride concentration of water from this aquifer as would be expected if the aquiclude were leaking.
    The chloride content of the water increases southwestward, the general direction of water movement. The fresh water apparently mixes with saline water in the aquifer to account for the increase in chloride. Figure 6 shows the relation of the increase in total mineral


z
-J

W


0


400


300
              Only those samples containing greater
              than 5 ppmn chloride included 200


  100  _ _ _ __ _ _'.            __________           _ _ _ _


       O   100   200     300    400     O  500 60      00    80      o
                  MINERAL CONTENT, IN PARTS PER MILLION
Figure 6. Scatter diagram showing relation of chloride to total mineral content
    of water from the Floridan aquifer in the Econfina Creek basin area.

concentration of the water to the increase in chloride for all samples containing more than 5 ppm. chloride.
   Figure 7 is a block diagram of a section along the coast showing chloride concentrations and water producing intervals of wells pene-