AQUIFER AS THE FUNDAMENTAL UNIT IN HYDROSTRATIGRAPHY AND ITS IMPACT ON FLORIDA NOMENCLATURE

In hydrostratigraphy, the aquifer is not always recognized as the fundamental unit used to characterize the water-bearing units. An aquifer can be defined as the basic hydrostratigraphic unit used in describing and interpreting the hydrogeology of a region. This statement is supported by the methods in the North American Stratigraphic Code and also the definitions of a zone and aquifer system. A zone is a subdivision of an aquifer and an aquifer system is two or more aquifers that serve as a water-bearing hydrostratigraphic unit. These definitions indicate that an aquifer or group of aquifers must be present for a zone or aquifer system to exist. Therefore, the aquifer should be considered the fundamental unit in defining and describing hydrostratigraphic units.

The three main hydrostratigraphic units in Florida are the surficial aquifer system, the intermediate aquifer system/intermediate confining unit, and the Floridan aquifer system. Inconsistencies related to ranking and application of the aquifer as the fundamental hydrostratigraphic unit results in the present classification of hydrostratigraphic units in Florida. Throughout large parts of Florida, the surficial aquifer system does not contain multiple aquifers and, therefore, does not rank as an aquifer system. The aquifer system rank can be applied if multiple aquifers are present in the hydrostratigraphic unit recognized as the surficial unit.

The intermediate aquifer system, in southwest Florida, contains up to three water-bearing units. The prevalent way of ranking these water-bearing units has been as zones. Aquifer systems require two or more aquifers to be present separated at least locally by a confining unit. No aquifers are identified in the intermediate aquifer system. The hydrostratigraphic units ranked as zones should be ranked as aquifers. In regions where two or more aquifers are present and function as a water-bearing unit, the aquifers may be grouped and ranked as an aquifer system. The ranking inconsistencies result from the oversight of the aquifer as the fundamental unit of hydrostratigraphic classification. The changes to the ranking of hydrostratigraphic units underlying Florida described here should be considered as part of the current practices in ranking of these units in the United States.