Hydrogeochemistry and cation-exchange processes in the coastal aquifer of Mar Del Plata, Argentina

Abstract

The aquifer of Mar del Plata is unconfined and composed of silt and fine sand. The sand fraction is mainly quartz, potassium feldspars, chalcedony, and gypsum. Volcanic-glass shards (40-60%) dominate the silt fraction, and the clays are of the smectite and illite groups. Calcium carbonate, in caliche form, constitutes about 10-20% of the sediment.Groundwater flow is from west to east, and discharge is in the Atlantic Ocean. Because of overexploitation, the flow direction was reversed in a coastal belt about 3.5 km wide, and this has resulted in seawater intrusion. The groundwater is the CaHCO 3 type in the recharge zone, and becomes NaHCO 3 type towards the discharge area. Salinization by marine intrusion and seawater/ fresh-water mixing produces an increase in the major-ion concentrations of the groundwater. The calcium content of the groundwater is higher and the sodium content is lower than those that would be expected if the mixing is considered as just the addition of seawater and fresh water in determined proportions without reactive processes taking place.Hydrogeochemical modeling was applied to the study of hydrogeochemical processes, mainly cation exchange, using the codes NETPATH and PHREEQM. Calcite and gypsum equilibrium, together with cation exchange, are the main hydrogeochemical processes. Cation-exchange capacity of the solid phase was determined by empirical calculations and experimental methods. The affinity order for the groundwater in contact with the aquifer ma-trix is Ca>Mg>Na in the regional-flow system, but the order is reversed in the salinization process. Reactive transport modeling using the code PHREEQM is useful for analyzing cation exchange in a marine-intrusion process.

Evaluation of Groundwater Suitability for consumption in Yaychi area (Southwest Kirkuk city - North Iraq)

“…We observe there are increases in the wet period as a result of the washing the salts of soil by runoff of rain with the remains of fertilizers and pesticides, and also due to sulfur production firm in the area which increase of sulfur ratio in the soil then reacts with the rainwater. All groundwater samples are classified as slightly brackish water except samples (3,6,8,17) in the dry period and (3,6) in the wet period classified as fresh water according to [19], depending on TDS values, Table- Cations Calcium ion concentration is ranging from 55.68 to 238.6 ppm and from 100 to 561 ppm in dry and wet period, respectively, while magnesium ion concentration varies from 52.07 to 576.35 ppm and from 50.4 to 491.4 ppm in dry and wet period respectively. Sodium ion concentration range between 101.8 -754.95 ppm in dry period and 66-810 ppm in the wet period.…”

“…Assessment of the quality of groundwater depends on the chemical and physical parameters of water, which are controlled by climate factors, soil, topography and human activities and thus determine their use for different purposes [1]. Hydro geochemical processes which control the chemical composition of groundwater are precipitation, dissolution, ion exchange processes and the residence time [2,3]. The assessment of groundwater quality status is important for socioeconomic growth and development [4].…”

Identification of hydrogeochemical process linked to marine intrusion induced by pumping of a semiconfined mediterranean coastal aquifer

“…This deficit is usually linked to bacterial reduction processes (Bosch and Custodio 1993;Martinez and Bocanegra 2002;Yamanaka and Kumagai 2006), according to the reaction: 2CH 2 O ? SO 4 -2 ?…”

“…sequence should show a process of seawater intrusion (Martinez and Bocanegra 2002), with sampling points P-b and P-1 lying in the zone where the b Na and b Ca ? Mg trend lines intersect.…”

Seawater–freshwater mixing and resulting calcite dissolution: an example from a coastal alluvial aquifer in eastern South Korea

“…Mercado 1985, Barbecot et al 2000, Harbison and Cox 2002, Al-Agha and El-Nakhal 2004, Pulido-Leboeuf 2004, Sivan et al 2005, Mondal et al 2010, Panteleit et al 2011. Cation exchange between Ca 2+ in dilute groundwater and Na + in seawater is well known (Nadler et al 1980, Richter et al 1993, Petalas and Diamantis 1999, Martínez and Bocanegra 2002, Andersen et al 2005, Appelo and Postma 2005, Petalas and Lambrakis 2006). An increase of the ionic strength of groundwater by seawater mixing also may increase the solubility of some aquifer minerals.…”