78 REPORT OF INVESTIGATIONS No. 50
the piezometric surface had fallen to about 62 feet and a lake level of only 64.7 feet produced equilibrium between gains and losses.
Generally lakes having the least range in fluctuation arc those whose levels are mainly affected by the water table in areas of relatively flat terrain. Lakes Silver and Corrine are examples. These lakes have relatively impermeable bottoms. Their levels are always high above the piezometric surface which has no effect on them. Surface inflow is small in comparison to the size of the lakes and they have surface outlets which readily remove excess water. During droughts seepage into the lakes from the relatively stable water-table aquifer tends to offset evaporation losses. These characteristics tend to reduce the difference in the rates of gains and losses so that ranges in fluctuation are small. In areas where the range of fluctuation of the piezometric surface is small, the range in fluctuation of a lake is small, no matter how effective its connection to the artesian aquifer.
WATER QUALITY IN LAKES
In general, the water in lakes in Orange County is of suitable chemical quality for most purposes, however, in some lakes hardness, high color, low pH, and other factors limit the usefulness of the water. An exception is the water in Lake Poinsett at the southeastern corner of the county which becomes so highly mineralized during extended droughts due to inflow of salty artesian water that it is not useful for many purposes.
One or more water analyses were made from 12 lakes in the county during the investigation (figure 13). Four lakes were sampled several times during high and low stages; the results of the analyses of these samples are summarized in table 8.
The water in Lake Francis near Plymouth has the lowest mineralization and Spring Lake at Orlando has the highest mineralization except for Lake Poinsett. Table 12 gives analyses of Lake Francis and Spring Lake. The mineral content of the water in Lake Francis is low because the surrounding hills are composed of clean, practically insoluble sand which allows the rain to seep rapidly to the lake without becoming very mineralized and because downward leakage to the artesian aquifer prevents a buildup of mineralization. The relatively high calcium, sodium sulfate, and chloride concentrations in water from Spring Lake indicate that some pollution occurs. The sodium, sulfate, and chloride concentrations are all higher than they are in surface or ground