WATER RESOURCES OF ORANGE COUNTY 113
area-based on the configuration of the piezometric surface shown in figure 45-that might contribute recharge to the Floridan aquifer in Orange County.
Water level records of lakes, the nonartesian aquifer, and the Floridan aquifer show that lake levels and the water table are above the piezometric surface in most of Orange County (figs. 50 and 51) and rain will infiltrate and recharge the Floridan aquifer in most parts of the county if the confining bed overlying the aquifer is not impermeable. A study of the geologic logs of wells shows that the confining bed generally is much thinner and more permeable in the rolling highlands in the western part of the area than it is in the rest of the county (figs. 3, 6, and 39); therefore, rain can infiltrate to the Floridan aquifer much more easily in the highlands than in the lowlands.
i Analysis of the hydrographs of wells in the Floridan aquifer (figs. 37, 41, 52, and 53) and rainfall records show that the water levels in wells in the highlands respond to rainfall much more rapidly and with much greater magnitude than do wells in the rest of the county. This indicates that much more recharge is entering the Floridan aquifer in the highlands than elsewhere.
Another method of delineating recharge areas is by analysis of the mineral content of water from the aquifer. In general, water in recharge areas is less mineralized than in other areas. Therefore, if allowance is made for the varying solubilities of the materials in and above the aquifer and if there is no outside contamination, the less the mineralization of the water the closer it is to recharge areas. Figure 55 shows the dissolved solids in water in the aquifer in Orange County. The values when analyzed in conjunction with the piezometric maps indicate that there is an effective recharge area in and near western Orange County.
A third method of evaluating recharge areas is by computing the quantity of water which enters and leaves an area by underground flow. The difference between the two is the net recharge within the area. The net recharge plus any discharge (pumpage, spring flow or natural seepage) is the recharge within the area. The net recharge (outflow minus inflow) within Orange County was calculated to be an average rate of about 35 mgd in 1961. Pumpage was about 65 mgd, spring flow and seepage were estimated to be 110 mgd; therefore, total recharge was about 210 mgd. The weakness of this method is that the transmissibility
(T) of the aquifer may not be uniform and the T values used in the computation may not be representative of the aquifer.