118 REPORT OF INVESTIGATIONS No. 50
Floridan aquifer is less mineralized in western Orange County because it has been in the aquifer a short time. As the water moves eastward across the county, the dissolved solids gradually increase to about 500 ppm and then increase more rapidly to greater than 2,000 ppm, near the St. Johns River. The high mineral content of artesian water in the eastern part of the county is probably due in part to incomplete flushing of saline water that entered the aquifer when the sea last covered Florida.
Dissolved hydrogen sulfide gas is present in the water discharged by most of the wells penetrating the Floridan aquifer in Orange County, particularly water from the flowing, wells. Hydrogen sulfide gas has a very pronounced odor and gives water a pronounced taste. There are two possible sources of this gas in natural water. One is the reduction of sulfates by organic material under anaerobic (absence of oxygen) conditions, resulting in the decomposition of metallic sulfide by free carbon dioxide. In some cases hydrogen sulfide may be formed from the anaerobic reduction of organic matter with which the water comes in contact. The concentration of hydrogen sulfide in deep well water is highly variable, ranging from traces to over 4 ppm. Hydrogen sulfide is easily removed from water by aeration.
Figure 56 shows the hardness of water from wells that penetrate the Floridan aquifer in Orange County. The hardness of water in Orange County is caused almost entirely by the presence of calcium and magnesium salts. In the western and central parts of the county, the calcium and magnesium is combined with bicarbonate and the hardness is designated as carbonate hardness, formerly called temporary hardness. In eastern Orange County most of the calcium and magnesium in water from the Floridan aquifer is combined with chlorides and smaller amounts are combined with sulfates and bicarbonates. Hardness in excess of that combined with bicarbonate or carbonate is designated noncarbonate hardness, formerly called permanent hardness. The artesian water from well 832-056-1 in eastern Orange County had a hardness of 1,010 ppm and a noncarbonate hardness of 888 ppm which indicates that the calcium and magnesium is combined mostly with noncarbonate ions.
Figure 57 shows the range of chloride concentrations in water from the Floridan aquifer. The low concentrations of chlorides in the western and central parts of the county indicates that the sea water and residual salts have been completely flushed from the aquifer since this part of Florida was last covered by the sea.