Relation of carbon 14 concentrations to saline water contamination of coastal aquifers

Abstract

Naturally occurring stable or radioactive isotopes may be used in some places to identify the origin of saline water that contaminates some coastal aquifers. In a recent study to determine the origin of saline water in the Ocala Limestone aquifer near Brunswick, Georgia, the following sources were analyzed for C •4 and deuterium concentrations: potable water from the Ocala Limestone, contaminated water from the Ocala Limestone, saline water from the underlying Claiborne Group, and nearby ocean water. The chloride concentration of the groundwater ranges from about 25 ppm in the potable water to more than 20•g) ppm in the deeper part of the Claiborne Group. From an interpretation of piezometric maps and other hydrologic data, previous investigators had concluded that the source of the contaminating water was the Claiborne Group and not the nearby ocean. The essentially uniform range of low values of --965 to --987•o0 of the modern standard (National Bureau Standard C •4 oxalic acid) for the C • activity of the groundwater samples (regardless of the degree of contamination) is in agreement with this conclusion. If recent ocean water, which had a C • value of q-285•o0, were the source of contamination, the contaminated water would have had a C • activity higher than the activity of the fresh water. Deuterium analyses are not inconsistent with the interpretation that water from the Claiborne Group, rather than recent ocean water, is the source of the contaminating water. q•he concurrence of the hydrologic and the isotopic data in this area where the hydrology is well known suggests that isotopic analysis may be used to identify the origin of water in different pertions of a hydrologic environment.

Geochemical and boron, strontium, and oxygen isotopic constraints on the origin of the salinity in groundwater from the Mediterranean Coast of Israel

“…The evidence that several saline spots with high salinity existed since the 1930s [Vengosh et al, 1996] suggests that this salinization process is a natural phenomenon. It should be noted that salinization resulting from substantial quantities of saline water that flow upward because of a fault system that breaches impermeable units was also demonstrated in the upper Floridan aquifer in Georgia [Hanshaw et al, 1965;Krause and Randolph, 1989;Maslia and Prowell, 1990].…”

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

“…The large area of slightly higher Na+ concentrations centered near Brunswick, Ga., is due to upward seepage of deeper saline water induced by many years of heavy pumpage. The hydraulic effects of the pumpage are discussed in detail by Krause and Randolph (in press); earlier studies of the chemical effects of pumpage in the Brunswick area emphasized local increases in chloride concentration (Wait, 1965;Gregg and Zimmerman, 1974). The pattern shown in plate 4 is not exactly duplicated in plate 6 because the maps were drawn with different ranges of concentration.…”

“…Similarly, long-term pumpage in coastal cities of southeastern Georgia and northeastern Florida has caused decline of the freshwater head in the Upper Floridan aquifer. In this area, however, the decline in head has induced upward migration of brackish water DESCRIPTION OF GROUND-WATER CHEMISTRY (Stewart, 1960;Wait, 1965;Gregg and Zimmerman, 1974;Fairchild and Bentley, 1977;Leve, 1983). The possibility that lateral seawater encroachment could affect CP concentrations along the coast of southeastern Georgia and northeastern Florida was discounted by Johnston and others (1982) because the freshwatersaltwater interface in the Upper Floridan aquifer is more than 50 mi offshore from Jacksonville, Fla.…”

A study of saline incursion across an inter‐tidal zone on Anglesey, Wales using airborne conductivity data

“…The resolution required to fully interpret the model results discussed here would require further borehole assessments. These would typically involve downhole conductivity measurements and, potentially, isotopic (e.g., carbon‐14) dating of the pore fluids (Hanshaw et al 1965; Post et al 2003).…”