Geochemistry of the Floridan aquifer system in Florida and in parts of Georgia, South Carolina, and Alabama

Abstract

The Regional Aquifer-System Analysis (RASA) Program was started in 1978 following a congressional mandate to develop quantitative appraisals of the major groundwater systems of the United States. The RASA Program represents a systematic effort to study a number of the Nation's most important aquifer systems, which in aggregate underlie much of the country and which represent an important component of the Nation's total water supply. In general, the boundaries of these studies are identified by the hydrologic extent of each system and accordingly transcend the political subdivisions to which investigations have often arbitrarily been limited in the past. The broad objective for each study is to assemble geologic, hydrologic, and geochemical information, to analyze and develop an understanding of the system, and to develop predictive capabilities that will contribute to the effective management of the system. The use of computer simulation is an important element of the RASA studies, both to develop an understanding of the natural, undisturbed hydrologic system and the changes brought about in it by human activities, and to provide a means of predicting the regional effects of future pumping or other stresses. The final interpretive results of the RASA Program are presented in a series of U.S. Geological Survey Professional Papers that describe the geology, hydrology, and geochemistry of each regional aquifer system. Each study within the RASA Program is assigned a single Professional Paper number, and where the volume of interpretive material warrants, separate topical chapters that consider the principal elements of the investigation may be published. The series of RASA interpretive reports begins with Professional Paper 1400 and thereafter will continue in numerical sequence as the interpretive products of subsequent studies become available.

Ground water in freshwater-saltwater environments of the Atlantic Coast

“…20A), where the Upper Floridan aquifer is extensively confined and ground-water flow is quite sluggish. Because of the slow movement of ground water in the area, it is thought that residual seawater that entered the aquifer during the Pleistocene when sea level was higher than its current level has not been completely flushed out by modern freshwater (Sprinkle, 1989;Johnston and Bush, 1988;Reese, 1994Reese, , 2000Reese and Memberg, 2000). The anomalously high concentrations of chloride along the St. Johns River and the eastern coast of Florida are thought to be the result, in varying amounts, of two processes (Sprinkle, 1989): (1) incomplete flushing by the modern-day freshwater flow system of residual seawater that invaded the aquifer during high sea-level stands…”

Hydrogeology and the distribution and origin of salinity in the Floridan aquifer system, southeastern Florida

“…Miller (1986) studied the hydrogeologic framework of the Floridan aquifer system in the RASA study area (Florida and parts of Georgia, Alabama, and South Carolina), subdivided the aquifer system into chronostratigraphic units, and constructed hydrogeologic sections, isopach maps, and structure maps. Additional studies of the same area were conducted by Bush and Johnston (1988) and Sprinkle (1989). Bush and Johnston (1988) described ground-water hydraulics, regional flow, and changes in the flow system as a result of ground-water development of the Floridan aquifer system.…”

“…The depth of the base was determined using sample data or by calculation using predevelopment freshwater heads. The altitude of the base of freshwater flow determined by Sprinkle (1989, fig. 23) is similar to the altitude of the base of the brackish-water zone shown in figure 15.…”

“…Bush and Johnston (1988) described ground-water hydraulics, regional flow, and changes in the flow system as a result of ground-water development of the Floridan aquifer system. Sprinkle (1989) examined the geochemistry of the Floridan aquifer system and mapped the concentrations of selected constituents in water from the Upper Floridan aquifer. Results of the study by Sprinkle (1989, pi.…”

“…The altitude of the base of freshwater flow in the Floridan aquifer system was mapped by Sprinkle (1989, fig. 23).…”