A Geochemical Approach to Determine Sources and Movement of Saline Groundwater in a Coastal Aquifer

Abstract

Geochemical evaluation of the sources and movement of saline groundwater in coastal aquifers can aid in the initial mapping of the subsurface when geological information is unavailable. Chloride concentrations of groundwater in a coastal aquifer near San Diego, California, range from about 57 to 39,400 mg/L. On the basis of relative proportions of major-ions, the chemical composition is classified as Na-Ca-Cl-SO 4 , Na-Cl, or Na-Ca-Cl type water. δ 2 H and δ 18 O values range from −47.7‰ to −12.8‰ and from −7.0‰ to −1.2‰, respectively. The isotopically depleted groundwater occurs in the deeper part of the coastal aquifer, and the isotopically enriched groundwater occurs in zones of sea water intrusion. 87 Sr/ 86 Sr ratios range from about 0.7050 to 0.7090, and differ between shallower and deeper flow paths in the coastal aquifer.3 H and 14 C analyses indicate that most of the groundwater was recharged many thousands of years ago. The analysis of multiple chemical and isotopic tracers indicates that the sources and movement of saline groundwater in the San Diego coastal aquifer are dominated by: (1) recharge of local precipitation in relatively shallow parts of the flow system; (2) regional flow of recharge of higher-elevation precipitation along deep flow paths that freshen a previously saline aquifer; and (3) intrusion of sea water that entered the aquifer primarily during premodern times. Two northwest-to-southeast trending sections show the spatial distribution of the different geochemical groups and suggest the subsurface in the coastal aquifer can be separated into two predominant hydrostratigraphic layers.

Residence time, mineralization processes and groundwater origin within a carbonate coastal aquifer with a thick unsaturated zone

“…Indeed, the groundwater residence time documents on contaminant transport and sustainability of water resources (Baudron et al, 2014;Cook et al, 1995;Cook and Herczeg, 2000;Gourcy et al, 2009;Murgulet et al, 2016;Vautour et al, 2015). It is also a powerful integrative approach of groundwater origin and flow path organisation within aquifers (Anders et al, 2014;Bertrand et al, 2010;Gooddy et al, 2006;Jaunat et al, 2012;Kamtchueng et al, 2015). Furthermore, groundwater residence time provides information to constrain recharge area, discharge rate, flow directions and velocities, all necessary to either quantitatively validate a numerical or conceptual hydrogeological model Post et al, 2013;Turnadge and Smerdon, 2014;Zuber et al, 2005).…”

Isotope signatures and hydrochemistry as tools in assessing groundwater occurrence and dynamics in a coastal arid aquifer

“…Cl/Br ratios in coastal groundwaters are typically close to 290 (Davis et al 1998;Anders et al 2014). Since Br is slightly more soluble than Cl, the Cl/Br ratio in evaporates (halites, gypsum) decreases due to evaporative effects.…”

“…Since Br is slightly more soluble than Cl, the Cl/Br ratio in evaporates (halites, gypsum) decreases due to evaporative effects. In consequence, the dissolution of these rocks may increase the ratio to 4000 (Davis et al 1998;Anders et al 2014). Wastewater loaded with NaCl may increase the ratio up to 655.…”

Hydrochemical Facies and Ionic Exchange in Coastal Aquifers of Puducherry Region, India: Implications for Seawater Intrusion

“…Salinization of groundwater is controlled by factors like seawater intrusion, rock-water interaction, over exploitation, rise in sea level, climatic changes, hydrogeological setting of the study area, salt panning, improper sewage disposal, use of chemical fertilizers and pesticides, marine formations, etc. (Nair et al 2015;Batayneh et al 2014;Anders et al 2013;Amiri et al 2015). Among all these factors, seawater incursion is considered to be a major threat to coastal aquifers globally.…”

“…There are several methods that can be adopted for studying salinization of groundwater like hydrochemical facies evolution method (Giménez-Forcada 2014); freshwater-seawater interaction (Mondal et al 2010a, b); isotopic techniques (Anders et al 2013); ionic ratios (Batayneh et al 2014;Chen and Jiao 2007); and geophysical surveys (Ayolabi et al 2013). The main purpose of this study is (1) to understand theevolution of hydrochemical facies during intrusion and freshening phase using hydrochemical facies evolution-diagram and (2) to determine the amount of seawater incurred into groundwater using empirical hydrochemical data, by which seawater ingress into the coastal aquifers of Puducherry region can be traced out spatially and temporally.…”