Perdido River and Bay - Florida Department of Environmental ...

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32 Water Quality Status Report: Perdido River and Bay seagrasses between 1941 and 1992 revealed that total bay acreage had decreased by 74 percent to about 307 acres (Kirschenfeld, Turpin, and Handley, 2006). More recent seagrass coverage analysis completed in 2003 found 300 acres of shoal grass in the bay (Gulf of Mexico Program Habitat Team, 2004). Seagrasses provide spawning, nursery, and adult habitat for many commercially and recreationally important species. The Perdido Basin provides habitat for several rare and imperiled fish species. Three rare fish species were historically noted from the Perdido River. These include the listed species of special concern saltmarsh topminnow (Fundulus jenkinsi), crystal darter (Crystallaria asprella), and goldstripe darter (Etheostoma parvipinne) (DNR, 1989). Bass, Hoehn, Couch, and Mcdonald (2004) confirmed the presence of the saltmarsh topminnow during field sampling in 2001 to 2002 in tributaries of the Perdido Bay watershed. Striped bass use the Perdido River throughout its length (DNR, 1989). The Gulf race of the Atlantic sturgeon (Acipenser oxyrinchus de sotoi) utilizes the Perdido River as documented by the Alabama Geological Survey in 2004 (referenced in Bass et al., 2004). Ground Water Resources Aquifers Major aquifer systems in the basin are the sand and gravel aquifer (local surficial aquifer system), the intermediate aquifer system, and the Floridan aquifer system. Both the sand and gravel aquifer and the Floridan aquifer systems are composed of moderate to highly permeable sediments that transmit large quantities of water. In contrast, the inter mediate aquifer system and the sub-Floridan systems are composed primarily of lowpermeability sediments that act as regional confining units. The sand and gravel aquifer extends under all or part of Escambia, Santa Rosa, Okaloosa, and Walton Counties, eastward to the Choctawhatchee River. The sand and gravel aquifer is comprised of interbedded unconsolidated quartz sand with some gravel, clay, and silt that range in age from the middle Miocene to Holocene (USGS, 1990). Ground water exists in this aquifer under unconfined to semiconfined conditions. Beds and lenses of clay interspersed with gravel form confi ning beds to create local artesian conditions. In Escambia County, the sand and gravel aquifer is informally divided and named into three distinct zones (Pratt, Richards, Milla, Wagner, Johnson, and Curry, 1996). The uppermost zone, called the surficial zone, is primarily composed of fi ne sands and is usually under unconfined conditions (Paulic, 1999). Below the surficial zone is a low-permeability zone. As a semiconfining layer, it impedes the downward flow of ground water. The third and deepest zone is the main producing zone, which is composed of very permeable coarse sand and gravel beds interspersed in places with fine sand and clay-sand beds. Most potable drinking water for Escambia County is obtained from the main producing zone. This aquifer is recharged directly by rainfall. The entire geographic extent of the sand and gravel aquifer is in effect a recharge area (Pratt et al., 1996). The primary flow of ground water in the aquifer is laterally toward surface waters and the coast (Richards, 1998; USGS, 1990) providing
Water Quality Status Report: Perdido River and Bay 33 discharge or baseflow into streams, lakes, and the Gulf of Mexico. Wells also indirectly discharge a small amount of water to surface waters. The closeness with the land surface makes the sand and gravel aquifer highly vulnerable to contamination. Surface spills and poor waste disposal methods can easily allow contaminants to infiltrate into this aquifer. Below the sand and gravel aquifer lies the intermediate aquifer system, which acts as a thick confining unit between the sand and gravel aquifer and the Floridan aquifer system in most of the basin. Composed of thick beds of clays, along with clayey limestone, shells, and coarse clastics of Miocene age, the intermediate system prevents most exchange of ground water between the two aquifer systems (Richards, 1998; Ryan, MacMillan, Pratt, Chelette, Richards, Countryman, and Marchman, 1998; Pratt et al., 1996). The Floridan aquifer system, underlaying the intermediate system, consists of a thick sequence of carbonate rock of varying permeability and a regionally extensive clay confining layer. The top of the Floridan aquifer system ranges from near sea level at the eastern boundary of the basin to over 1,000 feet below sea level at the western boundary (Pratt et al., 1996). Ground Water Usage The primary source of drinking water in Escambia County is the main producing zone of the sand and gravel aquifer (Pratt et al., 1996). The Floridan aquifer is deep, approximately 350 feet below sea level in northeast Escambia County to 1,450 feet below sea level in the southwest, and its water is brackish and highly mineralized. Surface water is used for power generation and some commercial and industrial self-supply. There are 25 wells in the Perdido Basin identified in the Department’s Public Water System database as public water supply wells (Figure 2.5). The largest water supply system, Emerald Coast Utilities, has 13 wells. Public supply wells in the basin range between 192 and 415 feet in depth, with an average well depth of 255 feet. The largest consumer of water from the sand and gravel aquifer is International Paper, which utilizes approximately 24.7 million gallons per day (Pratt, Richards, and Milla, 1997). The discharge from International Paper is currently released into the Perdido River. A new discharge permit proposed in April 2005 requires that the facility discharge be moved to a treatment wetland. Additional information on International Paper’s permit conditions is contained in the “Perdido Bay Planning Unit” section contained in Chapter 3. Ground Water–Surface Water Interactions The sand and gravel aquifer is the main source of baseflow for wetlands, streams, and lakes in the basin. Because the intermediate is an effective confining unit, much of the recharge to the sand and gravel aquifer ends up as discharge to surface waters. Stream baseflow is substantial and has been estimated by Vecchioli, Tibbals, Duerr, and Hutchinson (1990) as exceeding 1 cubic foot per second per square mile. Model estimates of a ground water budget for the aquifer’s main producing zone in Escambia County indicate that more than 50 percent of the recharge received in this
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