WATER RESOURCES OF ORANGE COUNTY 91
from a 75-foot deep well at Bithlo (832-105-2) constructed in a secondary artesian aquifer had a dissolved solids content of 380 ppm. The water from an adjacent 492-foot deep well in the Floridan aquifer had a dissolved solids content of 290 ppm.
FLORIDAN AQUIFER
The principal artesian aquifer in Orange County is part of the Floridan aquifer that underlies all of Florida and parts of Alabama, Georgia, and South Carolina. The Floridan aquifer, as defined by Parker (1955, p. 189) includes "parts or all of the middle Eocene (Avon Park and Lake City limestones), upper Eocene (Ocala limestone), Oligocene (Suwannee limestone), and Miocene (Tampa limestone) and permeable parts of the Hawthorn formation that are in hydrologic contact with the rest of the aquifer."
AQUIFER PROPERTIES
The Floridan aquifer is one of the most productive aquifers in the country. In Orange County many large diameter wells (20 inches or more) yield more than 4,000 gpm. These wells can be constructed in almost any area of the county. Wells that will yield only small quantities of water are usually in the vicinity of sinkholes where sand has filled solution channels in the aquifer. Pumping rate-drawdown ratios range from less than 100 gpm per foot of drawdown to over 500 gpm per foot of drawdown. The aquifer consists of nearly 2,000 feet of porous limestone and dolomite or dolomitic limestone covered by sand and clayey sand ranging in thickness from a few feet to about 350 feet. The altitude and configuration of the top of the Floridan aquifer is shown in figure 38. The depth below land surface to the top of the aquifer is shown in figure 39. The total thickness of the aquifer is not accurately known because the deepest water well in the county penetrates only the upper 1,400 feet. The log of an oil test hole drilled southeast of Orlando shows dense anhydrite at about 2,000 feet, and this is assumed to be the base of the aquifer.
The lithologic and hydrologic character of the Floridan aquifer is not uniform either horizontally or vertically. In general, there are alternating layers of limestone and dolomite or dolomitic limestone. The limestone layers are usually softer and of lighter color than the dolomitic layers. The aquifer stores huge quantities of water and also acts as a conduit. Water moves slowly through