The closed depressions shown on the Citrus County map to the right are the relics of fractures and ancient sinkholes in the underlying limestone that over time have filled with primarily sand. These are now filled with water.
The water in these closed depressions directly feed our springs and the Aquifer from where we draw our drinking water. Road grime and other pollution that wash into the closed depressions end up directly in our springs and wells.
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The Suncoast 2 is being proposed on top one of the largest recharge system for the Florida Aquifer in West Central Florida.
In the map at top, the path of the proposed alignments for the Suncoast Parkway 2 is superimposed in red. The closed depressions are shown in bright blue.
What we see as hills and valleys today, especially in the Central Ridge area of the county, are actually the results of these geological processes. These valleys are an integral part of the Floridan Aquifer and in particular, the Brooksville Ridge in Citrus County.
The Floridan Aquifer is essentially karst limestone, a water-bearing rock. It is composed of distinct limestone formations that have an embedded network or matrix of holes, conduits or caves, and cracks. Rainwater seeping down, through these sands recharges the Floridan Aquifer. Closed-depressions in essence act as a sand- filled funnel directly feeding into the Floridan Aquifer.
Closed depressions are created through a complex process taking place over millions of years going back to the origins of peninsular Florida itself. As rain falls and seeps down through the soil, water combines with carbon dioxide in the air to form a very weak solution of carbonic acid. This acid slowly dissolves erratically the limestone forming what is called karst limestone, rock filled with cavities and caverns or pockets that can hold water.
Over time, these small cracks and holes expand at an accelerated rate as more mildly acidic water flows through them. As more cracks or faults develop from literally earthquakes or tectonic plate movement in the parent base rock , these voids and cavities become increasingly interconnected and form an underground network of "pipes" through which groundwater flows within the rock of the Aquifer. (see Types, Features, and Occurrence of Sinkholes in the Karst of West-Central Florida, USGS Report 85-4126, USGS and SWFWMD, 1985)
First Magnitude Springs
Water flows underground just as it does on the surface, from higher elevations to lower elevations. The pressure from the weight of the water in the Aquifer above the elevation level of the springs is what "pushes" water through the spring heads. Elevations of the bottom of closed-depressions on the Brooksville Ridge are roughly 50 feet above sea level with hills adjoining them of often over 150 feet above sea level within less than a quarter of a mile. The springs on the other hand are at a level of usually a minimum of 8 feet below sea level, some almost 40 below MSL. If you froze for a second this dynamic system, the analogy would be a 58-foot high water tower with a hose going to the bottom of the spring.
The Brooksville Ridge
On the Brooksville Ridge (see below) unlike most other places in Florida, there is no confining layer of clay or non-porous rock that slows down the seepage of water into the Aquifer. In fact the karst is completely exposed in many areas on the coast and Withlacoochee River. The "pushing" action of the water column therefore is unimpeded; it's just going through sand. The result is the multitude of first-magnitude and smaller springs immediately west of the Brooksville Ridge, in some places only a few miles away. To be classified as a first-magnitude spring, a spring must discharge on average 65 million gallons of water per day. The Brooksvile Ridge and coastal springs are therefore not isolated geological and hydrological phenomena but an integrally connected system. They are globally unique in fact.
Because of this unique system, pollution that could flow into the closed depressions would flow directly into and through the Floridan Aquifer and pollute the springs. This transfer would be rapid, up to 9,000 feet per day, and has been documented for inorganic fertilizers already in several scientific studies, some financed by SWFWMD. The formation of these closed-depressions is documented as well on pages 3-5 and 3-6 in the Conservation Element of the Citrus County Comprehensive Plan.