Protection Standards and Best Management Practices

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Guidance

FDEP/DCA publish an Implementation Guidebook to municipality and county administrations for the protection of springs. Click here to see the full text of the Guidebook.

There are several elements of the natural environment that are important for an understanding of the aquifer system. First, the karst limestone formations of the Floridan Aquifer system are very highly porous and permeable. The caves at springs and dry caves are the large, visible aspects of this feature. Small and large interconnected fractures, solution cavities, and a very porous nature at the microscopic level enable the aquifer to store very large volumes of water and allow water to flow quite freely through the aquifer. In discharge areas, the pressure in the aquifer forces water up through the soils and sandy overburden covering the rock, creating wetlands or augmenting stream flows.

A Springshed is the area of land whose water will eventually end up in a spring or spring run. The shape of this recharge area, or springshed, is influenced not only by topography but also by what is happening unseen under the ground - the presence of cave systems, fissures and other karst features.

The federal Clean Water Act recognizes subterranean tributaries conveying water via submersed spring vents into a surface water – as into the Outstanding Florida Water of Crystal River/Kings Bay. Those tributaries pose the same relative vulnerability to contamination of the aquifer as any other aquifer feature.

DRASTIC indexes

The U.S. Environmental Protection Agency (EPA) has identified the following seven key factors that determine aquifer vulnerability: (1) Depth to ground water; (2) Recharge rate to ground water; (3) Aquifer media; (4) Soil type; (5) Topography; (6) Impact of the vadose zone; and (7) Conductivity of the aquifer. Each of these factors is assigned a combination of weights and ratings, and a numerical index, called the DRASTIC index, is computed and used to evaluate the relative vulnerability of different aquifers or different segments of a given aquifer.

DRASTIC index values range from 0 to about 250; the larger the index, the greater is the relative vulnerability of the aquifer to contamination. In some areas, the aquifer is overlaid with deposits of permeable sand and is easily and directly recharged. A high DRASTIC index of 224 suggests that ground water contamination is highly likely in this area. In contrast, a thick deposit of impermeable clay over the aquifer will result in a lower DRASTIC index of 150, indicating a much lower vulnerability to contamination.

Subterranean tributaries are often comprised of parallel fractures each of which subtends a Zone of Influence according its depth, enabling the tributary to drain fluids from an area of a few to hundreds of meters wide of its indicated path. It follows that in order to define the limits for a protection zone for an indicated subterranean tributary a profile of DRASTIC indexes should be calculated across the width of the tributary.

Having such protection zones scientifically defined will facilitate permitting decisions to be taken in the public interest according to the Florida Anti-degradation Policy (62-302.300 and 62-4.242 F.A.C.) and following precepts contained in the FDEP/DCA Guidebook.