THE HAWTHORN AQUIFER SYSTEM: A PROPOSAL FOR HYDROSTRATIGRAPHIC NOMENCLATURE REVISION IN SOUTHWEST FLORIDA

The intermediate aquifer system has been the hydrostratigraphic unit name proposed for aquifers occurring between the overlying surficial aquifer system and underlying Floridan aquifer system in Florida since 1986. The aquifers and confining units present in the intermediate aquifer system are composed of interbedded carbonate and siliciclastic sediments predominantly within geologic formations of the Hawthorn Group in southwest Florida. This aquifer system name has been used in publications for many years with a variety of naming conventions for permeable units that do not always follow nomenclatural guidelines. The resulting collection of hydrostratigraphic names for these units is as varied as the Hawthorn Group sediments that make up these aquifers and confining units in southwest Florida.

A region of southwest Florida with an area of 13,000 square kilometers (5,100 mi2), covering all or part of several counties contains the most productive aquifers in the Hawthorn Group sediments statewide. The distribution and hydrogeologic properties of these sediments have been extensively studied over the past 30 years. The majority of published studies have concluded that the significant permeable units or aquifers are composed of formation materials of the Hawthorn Group. Stratigraphic associations of aquifers and intervening confining units delineated in the Hawthorn Group sediments over much of this region constitutes an aquifer system, with as many as three distinct aquifers present in the region.

We are proposing that the name Hawthorn aquifer system be used to for all parts of this region where two or more aquifers are present. Aquifers of the Hawthorn aquifer system would be named after geologic formations in descending order: the Peace River aquifer, the upper Arcadia aquifer and the lower Arcadia aquifer. Positional references are relative only to the stratigraphic occurrences of the two distinct aquifers within the Arcadia Formation. Also, upper and lower confining units would not be included in the overall thickness of the Hawthorn aquifer system. Our proposed aquifer system naming convention will more accurately identify the stratigraphic relations of these units, and alleviate discrepancies in hydrostratigraphic nomenclature currently applied to this important aquifer system.