WATER RESOURCES OF ORANGE COUNTY 121
Eastward across the county the chloride concentration increases, which indicates incomplete flushing of the highly mineralized water from the aquifer. Of the wells inventoried in the county, artesian well 832-056-1 east of Christmas yielded water with the highest concentration of chloride (1,750 ppm). Well 832-053-1 in Brevard County yielded water with a chloride concentration of 6,200 ppm. Sea water contains an average of about 19,100 ppm chlorides.
Table 13 gives the analyses of water from selected wells in the Floridan aquifer in Orange County. Well 844-133-1 is in the northwestern part of the county and well 832-056-1 is a flowing well near the St. Johns River. Figure 58 shows the chemical composition of water from the selected wells listed in table 13. In figure 58 the bicarbonate is shown as carbonate. Carbonate is present in water when the pH value exceeds 8.2. Some of the artesian water in Orange County contains small amounts of carbonate, but most of the alkalinity is due to bicarbonate. Figure 58 shows that the artesian water in western Orange County is high in calcium bicarbonate whereas the highly mineralized water in the eastern part of the county is high in sodium chloride.
Mineralization of ground water generally, but not always, increases with depth. Figure 44 shows the relation of dissolved solids content and hardness of ground water to depth of wells in the Orlando area. Figure 44 shows that the water in the upper part of the Floridan aquifer (150-400 feet) in the Orlando area is slightly higher in mineralization than the deeper water (1,200-1,500 feet). The water is more mineralized in the upper part of the aquifer because the soft limestone is more soluble than the hard dolomitic limestone at the 1,200 to 1,500 feet level. However, the mineralization in the 400-600-foot dolomite zone is similar to the mineralization in the 1,200-1,500-foot dolomite zone.
The average calcium to magnesium ratio in water from the upper zone is 5.5 to 1 and the average calcium to magnesium ratio in water from the lower zone is 4.0 to 1. The lower calcium to magnesium ratio in the lower zone indicates that the limestone is dolomitic. Water in contact with pure dolomite usually has a calcium to magnesium ratio of about 3 to 1.
The water from one of the Orlando supply wells was analyzed for minor elements and the following results were obtained: Well: 833-122-13
Depth: 1,445 feet. Cased to: 945 feet
Diameter: 28 inches. Yield: 4,000 gpm
Temperature: 770F