FLORIDA GEOLOGICAL SURVEY


water-table aquifer. No difference in the chemistry of surface water in the basin was noted between high and low flow except for the color and pH. High color immediately following a rain is attributed to the flushing of the decayed organic material from the swampy, poorly drained areas adjacent to the streams. This same colored water tends to be acid due to the solution of carbon dioxide released from the decaying plants. The pH of the streams is lower (more acid) during high flow when the flushing of the swampy areas occurs. The pH normally ranges from 6.0 to 7.0 units but falls below 6.0 during these times.
   Two areas of exception to the normal low mineral concentration in stream water occur in the Econfina Creek basin. One of the areas is alona, Econfina Creek downstream from a point about due east of Porter Lake, where the creek receives flow from artesian spr ' ings. These springs emanate from limestones of the Floridan aquifer and the chemistry and relative solubility of the rocks are reflected in the mineral constituents found in the water. The mineral concentration in water from the springs ranged from 50 to 68 ppm and all but about 10 to 12 ppm were calcium and magnesium carbonate, the constituents of limestone. The mineral content of the water in Econfina Creek, downstream from where spring water enters, is higher than that in other stream in the basin, and varies with the ratio of spring flow to surface runoff. Calculations, based on chemical analyses, (see p- 84), show that 70 to 75 percent of the base flow of Econfina Creek at the Bennett gaging station is from springs.
   The other area of exception to normal low mineral concentrations in stream water is near the mouth of the streams which empty into salt-water bays. Salt water moves up the streams a distance that is dependent upon the elevation of the streambeds, the stage of the streams, and tides. This encroachment of saline water occurs in the mouths of allStTeams except those emptying into Deer Point Lake, which is a fresh water body.
   That part of the rainwater that replenishes the aquifers continues to move in the hydrologic cycle but at a slower rate than the water moving, as surface flow. This slow rate of movement allows a state of chemical equilibrium to be approached and normally results in ground water having a higher concentration of mineral constituents than does the surface water in an area. The highly insoluble nature of the sandswhich form the water-table aquifer in the Econfina Creek basin results in low mineral concentration of water in this aquifer. Generally, the concentration of total mineral constituents in water from this aquifer ranged from 10 ppm (about equal to that of rainwater)