The principal aquifer in the Orlando area consists of 900 feet or more of permeable artesian limestones of upper and middle Eocene age. As in most other parts of the Florida peninsula, these limestones are overlain by the Hawthorn formation of Miocene age which contains relatively impervious beds. The Hawthorn at Orlando is 45 to 200 feet thick and prevents or retards natural recharge to the lime. stones except where it is penetrated by what appear to be old sinkholes that are now filled with pervious material.

Owing to the lack of adequate surface drainage, more than 200 wells have been drilled into the limestones in the Orlando area to drain streets, control lake levels, and dispose of sewage and other waste liquids. Generally the piezometric surface of the water in the limestones is fat enough below the land surface to allow drainage by gravity. As the limestones are cavernous, most of the wells have large capacities for receiving water and seldom become clogged although a considerable amount of rubbish is carried into them.

The piezometric surface is conspicuously higher where drainage wells are concentrated, probably because of recharge through wells. However, the effect of the artificial recharge cannot be clearly differentiated from that of natural recharge. A deep-well current meter was used to determine the horizons at which the polluted surface water enters the limestones.

The investigation was made in cooperation with the Florida Geological Survey and the Corps of Engineers of the U.S. Army.